HIGH RPM WHILE SHIFTING

PonyGTrider · Dec 22, 2020

Hi all
I've read a lot of postings here and there about this issue without a conclusive solution.
I've done everything in the "Surging List" starting with scanning the system for error codes without results.
I've been driving my car with a IAC restriction shim or plate being this the only way to maintain the RPM's down while shifting and coasting.

Today I removed the plate trying to do more research on this issue, removed the restriction plate and sure enough the idle RPM hangs for a while before returning to the set idle.

I plugged the IAC valve and connected my voltmeter to the harness and started the engine. I observed that the voltage goes up when I snap the gas but takes a while to come down along with the RPM. is that NORMAL?

another observation was that the IAC valve it has an open air flow and the solenoid opens more that flow when the engine is running. I though the valve supposed to be closed and then start to open with a variably voltage thru the negative wire. In this video it seems to me that that IAC is fully closed and then the voltage opens it on demand?

View: https://www.youtube.com/watch?v=kVB6-aRKXUo

Can someone elaborate on this issue? Why the IAC restriction plate seems to help correcting this issue? Is this a flaw on the design , or is there a computer malfunction?

PonyGTrider · Dec 22, 2020

Hi all
I've read a lot of postings here and there about this issue without a conclusive solution.
I've done everything in the "Surging List" starting with scanning the system for error NO ERRORS..
I've been driving my car with a IAC restriction shim or plate being this the only way to maintain the RPM's down while shifting and coasting.

Today I removed the plate trying to do more research on this issue, removed the restriction plate and sure enough the idle RPM hangs for a while before returning to the set idle.

I plugged the IAC valve and connected my voltmeter to the harness and started the engine. I observed that the voltage goes up when I snap the gas but takes a while to come down along with the RPM. is that NORMAL?

another observation was that the IAC valve it has an open air flow and the solenoid opens more that flow when the engine is running. I though the valve supposed to be closed and then start to open with a variably voltage thru the negative wire. In this video it seems to me that that IAC is fully closed and then the voltage opens it on demand?

View: https://www.youtube.com/watch?v=kVB6-aRKXUo

Can someone elaborate on this issue? Why the IAC restriction plate seems to help correcting this issue? Is this a flaw on the design , or is there a computer malfunction?

HemiRick · Dec 22, 2020

The restrictor helps because it doesn't let the idle go above the size of the hole in it. I had one installed on my car for a long time, because it wanted to idle at 2600 and finally this winter removed it because my car was requiring several cold starts to stay running w it. I also installed a new MC IAC. It seems my original IAC was fine, as the new one changed nothing. My idle is now mostly ok with occasional high idle (1500-2600) still happening. It seems that resetting the ECU, seemed to help the most.

General karthief · Dec 22, 2020

Will the computer spit out codes?
You said you checked for codes and got nothing? It will give you a code regardless of conditions. Unless of course the computer is bad.
Did you have a thread here on this issue?

PonyGTrider · Dec 22, 2020

HemiRick said:
The restrictor helps because it doesn't let the idle go above the size of the hole in it. I had one installed on my car for a long time, because it wanted to idle at 2600 and finally this winter removed it because my car was requiring several cold starts to stay running w it. I also installed a new MC IAC. It seems my original IAC was fine, as the new one changed nothing. My idle is now mostly ok with occasional high idle (1500-2600) still happening. It seems that resetting the ECU, seemed to help the most.

Yeah I experienced the same

HemiRick said:
The restrictor helps because it doesn't let the idle go above the size of the hole in it. I had one installed on my car for a long time, because it wanted to idle at 2600 and finally this winter removed it because my car was requiring several cold starts to stay running w it. I also installed a new MC IAC. It seems my original IAC was fine, as the new one changed nothing. My idle is now mostly ok with occasional high idle (1500-2600) still happening. It seems that resetting the ECU, seemed to help the most.

Yeah I experienced the same effects, I know my IAC is fine but I wasn't sure if the valve supposed to be closed with no voltage running thru it, and still don't know
I made five plates with different breathing hole size, right now I have installed one in between the smaller and the next hole and my RPM's still hanging a bit high but I had installed the plate with the smallest hole and the engine would stall if trying to take off when cold

PonyGTrider · Dec 22, 2020

HemiRick said:
The restrictor helps because it doesn't let the idle go above the size of the hole in it. I had one installed on my car for a long time, because it wanted to idle at 2600 and finally this winter removed it because my car was requiring several cold starts to stay running w it. I also installed a new MC IAC. It seems my original IAC was fine, as the new one changed nothing. My idle is now mostly ok with occasional high idle (1500-2600) still happening. It seems that resetting the ECU, seemed to help the most.

General karthief said:
Will the computer spit out codes?
You said you checked for codes and got nothing? It will give you a code regardless of conditions. Unless of course the computer is bad.
Did you have a thread here on this issue?

I didn't say "Got nothing", I said NO ERROR. Well I'll rephrase that, No errors related to that issue. I got the typical errors related to the smog system deletion but don't think that will cause the high RPM while shifting or coasting in neutral problem, but not sure...

General karthief · Dec 22, 2020

PonyGTrider said:
starting with scanning the system for error codes without results.

Ok, let me clarify, people come on here all the time and say they 'get no codes' or 'didn't get anything' or something similar, I just wanted to be clear that a working computer will give you something, fault codes or a code that means 'system passed', your statement was not clear.
The surging idle checklist can help with a hanging idle problem if done step by step. I don't remember what year your car is but some have a VSS sensor on the trans where the speedometer cable attaches, this can cause a hanging idle when the car is in motion, then again you may have a vacuum leak someplace if it does it all the time.
What codes do you get when scanned?

PonyGTrider · Dec 23, 2020

Thank you I understand what you’re saying.
Mine is a 90 mustang GT and the codes I have are:
KOEO: 11
KOER: 44 - 94
Since the RPM stay high while shifting and while coasting in neutral position I thought about the VSS sensor or possibly the wiring, but never tested those two possibilities. Please share a procedure to do that...
In gear it feels as if I have the cruise control activated, and in neutral the RPM just stay high until I reach full stop then it falls to normal idle 850-900 RPM.
Have to state that there is no rolling idle just RPM hungs high.

Thanks for the help

General karthief · Dec 23, 2020

Have you replaced any of the gaskets like throttle body, egr plate and the upper to lower intake.

PonyGTrider · Dec 23, 2020

No gaskets have been replaced and following the surging checklist I inspected all the intake system and no vacuum leaks were found.

jrichker · Dec 24, 2020

PonyGTrider said:
Thank you I understand what you’re saying.
Mine is a 90 mustang GT and the codes I have are:
KOEO: 11
KOER: 44 - 94
Since the RPM stay high while shifting and while coasting in neutral position I thought about the VSS sensor or possibly the wiring, but never tested those two possibilities. Please share a procedure to do that...
In gear it feels as if I have the cruise control activated, and in neutral the RPM just stay high until I reach full stop then it falls to normal idle 850-900 RPM.
Have to state that there is no rolling idle just RPM hangs high.

Thanks for the help

Normal idle speed is 650-750 RPM; 850-900 RPM is way too high for normal operation.

IAC troubleshooting

Revised 24-Dec-2020 to clean up text and add SPOUT connector and Jumper picture.

IAC doesn't work: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An Oscilloscope is even better if you can find someone who has one and will help.

Automobile computers use current sink technology. They do not source power to any relay, solenoid or actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for the positive battery voltage to get back to the battery negative terminal. That flow of power from positive to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground provided by the computer, then the actuators and relays don't operate.

We are going to supply an artificial ground path to the IAC instead of letting the computer supply the ground.

Start the engine and let it warm up.

Take one of the cheap inline fuse holders with a 5 amp fuse in it. Use it to bypass the blue/white wire to ground. You'll have to get creative probing the back side of the IAC wiring with safety pins or paper clips. Since the computer doesn't supply any voltage, but supplies a ground, that can't hurt the computer. The 5 amp fuse protects you and the wiring if there is an internal short in the IAC coil.

The engine should speed up when the fuse holder wire is grounded and slow down or stall when the fuse holder wire is disconnected from ground.

Recommended procedure for cleaning the IAC/IAB:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damage some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. If it doesn't block the airflow, there is still something that is gumming up the works. Reassemble and reinstall to check it out.

Gunk Dip type carb & parts soaker:

Setting the base idle speed:
First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. If you have a wild cam, you may have to raise this figure 100-150 RPM or so. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s. This figure will increase if you have a wild cam, and may end up between 800-950 RPM

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work.
Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed.
SPOUT Connector

SPOUT Jumper

Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. A wild cam may make it necessary to increase the 600 RPM figure to 700 RPM or possibly a little more to get a stable idle speed.
Changing the mechanical adjustment changes the TPS, so you will need to set it. Anything between.6 and 1.0 volt is good. There is no advantage to setting it to .99; that is a BOZO Internet myth, complete with red nose and big floppy shoes.

When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads. A wild cam may make this figure somewhat higher.

PonyGTrider · Dec 24, 2020

jrichker said:
Normal idle speed is 650-750 RPM; 850-900 RPM is way too high for normal operation.

IAC troubleshooting

Revised 24-Dec-2020 to clean up text and add SPOUT connector and Jumper picture.

IAC doesn't work: look for +12 volts at the IAC red wire. Then check for continuity between the white/lt blue wire and pin 21 on the computer. The IAC connector contacts will sometimes corrode and make the IAC not work. The red wire on the IAC is always hot with the engine in run mode. The computer provides a ground for the current for the IAC. It switches the ground on and off, making a square wave with a varying duty cycle. A normal square wave would be on for 50% of the time and off for 50% of the time. When the idle speed is low, the duty cycle increases more than 50% to open the IAC more. When the engine speed is high, it decreases the duty cycle to less than 50% to close the IAC. An old-fashioned dwell meter can be used to check the change: I haven’t tried it personally, but it should work. In theory, it should read ½ scale of whatever range you set it on with a 50% duty cycle. An Oscilloscope is even better if you can find someone who has one and will help.

Automobile computers use current sink technology. They do not source power to any relay, solenoid or actuator like the IAC, fuel pump relay, or fuel injectors. Instead the computer provides a ground path for the positive battery voltage to get back to the battery negative terminal. That flow of power from positive to negative is what provides the energy to make the IAC, fuel pump relay, or fuel injectors work. No ground provided by the computer, then the actuators and relays don't operate.

We are going to supply an artificial ground path to the IAC instead of letting the computer supply the ground.

Start the engine and let it warm up.

Take one of the cheap inline fuse holders with a 5 amp fuse in it. Use it to bypass the blue/white wire to ground. You'll have to get creative probing the back side of the IAC wiring with safety pins or paper clips. Since the computer doesn't supply any voltage, but supplies a ground, that can't hurt the computer. The 5 amp fuse protects you and the wiring if there is an internal short in the IAC coil.

The engine should speed up when the fuse holder wire is grounded and slow down or stall when the fuse holder wire is disconnected from ground.

Recommended procedure for cleaning the IAC/IAB:
Conventional cleaning methods like throttle body cleaner aren’t very effective. The best method is a soak type cleaner used for carburetors. If you are into fixing motorcycles, jet skis, snowmobiles or anything else with a small carburetor, you probably have used the one gallon soak cleaners like Gunk or Berryman. One of the two should be available at your local auto parts store for $22-$29. Take the solenoid off the body and set it aside: the carb cleaner will damage some types of plastic parts. Soak the metal body in the carb cleaner overnight. There is a basket to set the parts in while they are soaking. When you finish soaking overnight, twist the stem of the IAB/IAC that sticks out while the blocker valve is seated. This removes any leftover deposits from the blocker valve seat. Rinse the part off with water and blow it dry with compressed air. The IAC/IAB should seal up nicely now. Once it has dried, try blowing through the bottom hole and it should block the air flow. If it doesn't block the airflow, there is still something that is gumming up the works. Reassemble and reinstall to check it out.

Gunk Dip type carb & parts soaker:

Setting the base idle speed:
First of all, the idle needs to be adjusted to where the speed is at or below 600 RPM with the IAC disconnected. If you have a wild cam, you may have to raise this figure 100-150 RPM or so. Then the electrical signal through the IAC can vary the airflow through it under computer control. Remember that the IAC can only add air to increase the base idle speed set by the mechanical adjustment. The 600 RPM base idle speed is what you have after the mechanical adjustment. The IAC increases that speed by supplying more air under computer control to raise the RPM’s to 650-725 RPM’s. This figure will increase if you have a wild cam, and may end up between 800-950 RPM

Remember that changing the mechanical idle speed adjustment changes the TPS setting too.

This isn't the method Ford uses, but it does work.
Do not attempt to set the idle speed until you have fixed all the codes and are sure that there are no vacuum leaks.

Disconnect the battery negative terminal and turn the headlights on. Leave the battery negative terminal disconnected for 5 minutes or so. Then turn the headlights off and reconnect the battery. This erases the computer settings that may affect idle performance.

Warm the engine up to operating temperature, place the transmission in neutral, and set the parking brake. Turn off lights, A/C, all unnecessary electrical loads. Disconnect the IAC electrical connector. Remove the SPOUT plug. This will lock the ignition timing so that the computer won't change the spark advance, which changes the idle speed.
SPOUT Connector

SPOUT Jumper

Note the engine RPM: use the mechanical adjustment screw under the throttle body to raise or lower the RPM until you get the 600 RPM mark +/- 25 RPM. A wild cam may make it necessary to increase the 600 RPM figure to 700 RPM or possibly a little more to get a stable idle speed.
Changing the mechanical adjustment changes the TPS, so you will need to set it. Anything between.6 and 1.0 volt is good. There is no advantage to setting it to .99; that is a BOZO Internet myth, complete with red nose and big floppy shoes.

When you are satisfied with the results, turn off the engine, and re-install the SPOUT and reconnect the IAC. The engine should idle with the range of 650-750 RPM without the A/C on or extra electrical loads. A wild cam may make this figure somewhat higher.

Thank you!
that is an extensive article and in the name of learning and finding some leads on why this common problem is occurring, I will tray to do those tests. At this point I was able to determinate that the computer is doing its job of adjusting the voltage at the IAC valve via the ground wire I pig-back my volt meter at the valve connector and I see the the voltage going up and down. Didn't write the numbers but I saw a bit over 1 Volt and as high as around 5 Volts (I believe)

Thanks again

PonyGTrider · Dec 24, 2020

With regard to the IAC valve I have a question:
My understanding and based on my observations if you start the engine with the valve is disconnected air still go thru the valve correct??? I have a total of five IAC valves and you can blow air thru the air passage and they only get fully sealed if you remove the solenoid or motor (Ad some people call it). So on an assembled valve when you start the engine there is already air flowing thru the valve and as the valve is energized by the computer it lets pass MORE air. Am I correct???
Please excuse me for so many questions but I’m just trying to make some sense about this valve operation.
Thank you all

jrichker · Dec 25, 2020

PonyGTrider said:
With regard to the IAC valve I have a question:
My understanding and based on my observations if you start the engine with the valve is disconnected air still go thru the valve correct??? I have a total of five IAC valves and you can blow air thru the air passage and they only get fully sealed if you remove the solenoid or motor (Ad some people call it). So on an assembled valve when you start the engine there is already air flowing thru the valve and as the valve is energized by the computer it lets pass MORE air. Am I correct???
Please excuse me for so many questions but I’m just trying to make some sense about this valve operation.
Thank you all

The mechanical adjustment of the idle set screw is supposed to set the low RPM minimum limit. A properly working IAC is supposed to add air to that minimum limit to bring the idle up to the 650-750 range.

This may work out to be trial and error method to get the results you want.
Therefore, test what you already have and see if you get the RPM down in the 600 +/- 25 range before you make any more changes.

If the gasket between the solenoid and IAC body is missing or too compressed, in many cases you can still blow air through the IAC. That may pass enough air to keep you from getting the RPM down in the 600 +/- 25 range.

If the IAC blocks airflow with the solenoid removed, you may need 2 gaskets to make it work properly. Or file a little metal off the solenoid plunger tip so that it will not pass air when you blow air through it. I would try the 2 gasket method first, since the results are easy to try and easy to reverse if it doesn't work like you want it to.

PonyGTrider · Dec 25, 2020

jrichker said:
The mechanical adjustment of the idle set screw is supposed to set the low RPM minimum limit. A properly working IAC is supposed to add air to that minimum limit to bring the idle up to the 650-750 range.

This may work out to be trial and error method to get the results you want.
Therefore, test what you already have and see if you get the RPM down in the 600 +/- 25 range before you make any more changes.

If the gasket between the solenoid and IAC body is missing or too compressed, in many cases you can still blow air through the IAC. That may pass enough air to keep you from getting the RPM down in the 600 +/- 25 range.

If the IAC blocks airflow with the solenoid removed, you may need 2 gaskets to make it work properly. Or file a little metal off the solenoid plunger tip so that it will not pass air when you blow air through it. I would try the 2 gasket method first, since the results are easy to try and easy to reverse if it doesn't work like you want it to.

Thank you for your reply,
And this opens a whole can of worms. I said I had five IAC valves but actually I have seven of them and none of them have a gasket in between the body and the solenoid there is only an O-ring, and they all have an open air flow thru them when assembled so besides the air flow thru the TB set opening of the butterfly there is an additional air flow thru the opened IAC valve. By God I thought the valve was supposed to be closed and the computer would do its job to open and close the valve on demand to maintain the idle RPM in check.

So By doing what you suggested, adding a gasket (which doesn't have) or reducing the plunger length with a file until the valve doesn't have free air flow when fully assembled, you will achieve my hypothesis. Am I correct?

On the two pics I'm showing what I'm saying:
First photo is the way the IAC valve comes assembled, No gasket
Second photo, there is > 0.100" gap between the solenoid and the body. That is how much the plunger is pushed in off its sealing position when assembled opening the valve airflow.

Is this a design flaw or this the way it supposed to be??? that is a hell of a question.

I'm sorry I'm writing too much, and thank you all for your patience.

PonyGTrider · Dec 25, 2020

PonyGTrider said:
Thank you for your reply,
And this opens a whole can of worms. I said I had five IAC valves but actually I have seven of them and none of them have a gasket in between the body and the solenoid there is only an O-ring, and they all have an open air flow thru them when assembled so besides the air flow thru the TB set opening of the butterfly there is an additional air flow thru the opened IAC valve. By God I thought the valve was supposed to be closed and the computer would do its job to open and close the valve on demand to maintain the idle RPM in check.

So By doing what you suggested, adding a gasket (which doesn't have) or reducing the plunger length with a file until the valve doesn't have free air flow when fully assembled, you will achieve my hypothesis. Am I correct?

On the two pics I'm showing what I'm saying:
First photo is the way the IAC valve comes assembled, No gasket
Second photo, there is > 0.100" gap between the solenoid and the body. That is how much the plunger is pushed in off its sealing position when assembled opening the valve airflow.

Is this a design flaw or this the way it supposed to be??? that is a hell of a question.

I'm sorry I'm writing too much, and thank you all for your patience.

Here the IAC valve with four layers of gasket material where the little piston of the solenoid just touches the valve body plunger and no airflow is open thru the valve. I will install it to see how it behaves. Good luck to me on this theory

PonyGTrider · Dec 26, 2020

PonyGTrider said:
Here the IAC valve with four layers of gasket material where the little piston of the solenoid just touches the valve body plunger and no airflow is open thru the valve. I will install it to see how it behaves. Good luck to me on this theory

I have an update on the test I run with the IAC with four paper gasket layers, and I'm a bit disappointed...

I disconnected the battery for about 10 minutes and then reconnected it back.
I installed the new set up IAC with the connector off and removed the distributor spout and warmed up the engine to OT. Then I set up the idle speed at the screw on the TB to ~650 RPM, then I set the TPS to 0.95 Volts and disconnected the battery again for 5 minutes.

Connected back the battery, connected back the distributor spout and plugged the IAC valve and started the engine.
I ran the engine for 2 minutes without any accessories ON. Turned it off for 2 minutes, then ran it for 2 minutes with all the accessories ON and then turned it off.
Started the engine and the RPM was about 700-750, then I took it for a ride. A few minutes of stop and go was fine then it just kept idling at about 1,200 RPM, staying there at every stop sign. Turned around and went back home. Removed the IAC and the flow was completely open :O :O

I disassembled the IAC valve and it seems like the plunger got stuck open I assembled it back and it was fine. Now I added one more layer of gasket material and assembled it back, everything is sealed and i tested it with a 9 Volts battery and it is opening and closing fine.

I'm going to give another shot and see if it works this time

Any comments and or suggestion will be appreciated

Thank you all

jrichker · Dec 27, 2020

PonyGTrider said:
I have an update on the test I run with the IAC with four paper gasket layers, and I'm a bit disappointed...

I disconnected the battery for about 10 minutes and then reconnected it back.
I installed the new set up IAC with the connector off and removed the distributor spout and warmed up the engine to OT. Then I set up the idle speed at the screw on the TB to ~650 RPM, then I set the TPS to 0.95 Volts and disconnected the battery again for 5 minutes.

Connected back the battery, connected back the distributor spout and plugged the IAC valve and started the engine.
I ran the engine for 2 minutes without any accessories ON. Turned it off for 2 minutes, then ran it for 2 minutes with all the accessories ON and then turned it off.
Started the engine and the RPM was about 700-750, then I took it for a ride. A few minutes of stop and go was fine then it just kept idling at about 1,200 RPM, staying there at every stop sign. Turned around and went back home. Removed the IAC and the flow was completely open :O :O

I disassembled the IAC valve and it seems like the plunger got stuck open I assembled it back and it was fine. Now I added one more layer of gasket material and assembled it back, everything is sealed and i tested it with a 9 Volts battery and it is opening and closing fine.

I'm going to give another shot and see if it works this time

Any comments and or suggestion will be appreciated

Thank you all

Changing the mechanical adjustment changes the TPS, so you will need to set it. Anything between.6 and 1.0 volt is good. There is no advantage to setting it to .99; that is a BOZO Internet myth, complete with red nose and big floppy shoes.

The instructions I posted said to set the base RPM at 600 RPM +/- 25 RPM.
Did you soak the IAC in the Gunk or Berryman carb cleaner?
IF not, the instructions may not work. Carbon and sludge build up over time and can make the IAC stick in one position.

PonyGTrider · Dec 27, 2020

jrichker said:
Changing the mechanical adjustment changes the TPS, so you will need to set it. Anything between.6 and 1.0 volt is good. There is no advantage to setting it to .99; that is a BOZO Internet myth, complete with red nose and big floppy shoes.

The instructions I posted said to set the base RPM at 600 RPM +/- 25 RPM.
Did you soak the IAC in the Gunk or Berryman carb cleaner?
IF not, the instructions may not work. Carbon and sludge build up over time and can make the IAC stick in one position.

Thanks for your reply.
“... Then I set up the idle speed at the screw on the TB to ~650 RPM, then I set the TPS to 0.95 Volts and disconnected the battery again for 5 minutes”

I did adjusted the TPS to 0.95 Volts.

No I didn’t soak the valve body in that solvent. The valve is nice and clean with no carbon buildup, I remember I shakes the valve hard so maybe the pintle had dislocated inside the solenoid piston.

Like I said I added a new layer of gasket material and tested it fully assembled with a 9 Volts and it opens and closes nicely.

This afternoon I installed the AIC valve with all the pertinent adjustments and the computer reset. I started the engine and it ran fine, tomorrow I will take it out to test and see how it behaves.

Thank you

General karthief · Dec 28, 2020

A couple things are nagging at me, have you changed the gaskets between the throttle body, egr valve and the intake? Do you have a nonstock cam in this?

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wonder how much it would cost to ship you a pair

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