Engine Erratic drop in idle when stopped

Mrg2783 · Jul 3, 2019

Hey Guys,

I'm stumped. I have code 11 and a 90 on the balance test. No stored codes. 11 across the board. It will do this for a minute or two then die.

I went through the Surging Idle Checklist and still cannot fix it I'm wondering if I have a valve sticking?

Replaced the upper intake gasket for the heck of it.

Checked all hoses and valve covers and to the best of my ability there are no vacuum leaks.

Oil looks nice and clean.

Replaced the IAC for a second time. (Hoping third time is a charm?)

Replaced the TPS for a second time.

Unplugged the EGR and plugged the vacuum line. Didnt help.

When I unplugged the IAC nothing happened?

I still need to unplug the Pro-M 80 MAF in my fender well which is brand new. So unless it just went bad after 500 miles pretty sure it's not the issue.

The car was recently dynoed and ran/runs great. Fires right up. Even after it dies from the idle issue.

This literally came out of nowhere one day when I was driving and pulled up to a light.

So I'm at a loss with no codes at this point, no leaks that I can find, good sensors.

I'm hoping your collective knowledge can point me in the right direction.

Any ideas are appreciated.

At this point I'm stumped. I cant figure it out. I have put in hours and hours and hours on this

View: https://youtu.be/9aI5FnnKJJ8

General karthief · Jul 3, 2019

Have you cleaned the maf sensor with the appropriate cleaner? If you are using a K&N filter and recently oiled it sometimes the oil gets on the sensor a messes it up.
What other mods do you have

Mrg2783 · Jul 3, 2019

General karthief said:
Have you cleaned the maf sensor with the appropriate cleaner? If you are using a K&N filter and recently oiled it sometimes the oil gets on the sensor a messes it up.
What other mods do you have

Thank you for the suggestion. Much appreciated.

I believe I may have fixed it. I put on an old IAC I had and the car seemed much more responsive right away. But it still was doing the idle drop.

Then I remember my dyno guy said my 284HR Blower cam was ideal at 1200 rpm idle.

My idle, for some reason, was at 950. I'm guessing the throttle body screw backed out. Sounds odd I guess. Who knows.

I made slight adjustments and got it back to 1200 and wahala. The idle drop is gone. She is running like a beast.

I'm not an expert obviously so if you or anyone has an explanation as to why to low of an rpm with my blower cam would cause severe idle drop issues. I would love to learn about it.

Thanks.

jrichker · Jul 3, 2019

With the idle speed set by tinkering with the idle stop screw to raise the idle speed above 650 RPM, the IAC/IAB computer control is inoperative. The IAC/IAB can only add air to increase the idle speed. It CANNOT decrease the airflow added by fiddling with the idle stop screw.

IAC troubleshooting

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. 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.

General karthief · Jul 3, 2019

You have a blower cam, do you have a blower?
My thoughts are you have developed a problem and upping the idle is just masking it.

Mrg2783 · Jul 3, 2019

General karthief said:
You have a blower cam, do you have a blower?
My thoughts are you have developed a problem and upping the idle is just masking it.

Yes, I have a Vortech V-1 running 7 psi.

I honestly worry that you are right lol

I am at a loss on what would have caused the issue.

This thing has been garaged its entire life, seen rain maybe 10 times. Every wire I have checked has always been in perfect working condition. Only 50,000 original miles. I rebuilt the motor from the heads out with all new sensors. Got her dynoed. She was perfect. Then the idle issue popped up at a light.

I guess I'll just drive it till something breaks lol

A 331 stroker with a V-1 TI at 15psi and a Magnum T56 are my future goal anyway. So screw it I guess. Over 300hrs in it at this point. I'm beat lol

But if you have any solid ideas let me know

Mrg2783 · Jul 3, 2019

jrichker said:
With the idle speed set by tinkering with the idle stop screw to raise the idle speed above 650 RPM, the IAC/IAB computer control is inoperative. The IAC/IAB can only add air to increase the idle speed. It CANNOT decrease the airflow added by fiddling with the idle stop screw.

IAC troubleshooting

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. 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 @jrichker. You're always on point.

So given what my dyno guy said about my cam and having the idle at 1200 because of my blower cam. Should I still go through the reset?

I tightened the throttle adjustment screw and raised the idle from 950 back to 1200 and idle drop is gone now. Also she runs tits. Doesnt feel like there are any throttle response issues etc.

Could I be masking a larger issue or should I just drive that B till something goes out?

jrichker · Jul 3, 2019

Mrg2783 said:
Thank you @jrichker. You're always on point.

So given what my dyno guy said about my cam and having the idle at 1200 because of my blower cam. Should I still go through the reset?

I tightened the throttle adjustment screw and raised the idle from 950 back to 1200 and idle drop is gone now. Also she runs tits. Doesnt feel like there are any throttle response issues etc.

Could I be masking a larger issue or should I just drive that B till something goes out?

Go through the process that I posted, it will help to sort out any unseen problems.

General karthief · Jul 3, 2019

First off let me thank you for making me feel kinda dumb, I would not have even responded to this if you had give accurate info on what the car had for modifications, I'm not a blower guy.
Modifications are a very important point when looking for help on an internet forum where the helper can't lay hands on the car to see what has been done.
I'm usually not brassy in my responses but in this case I will agree you need to drive it till it breaks.

Mrg2783 · Jul 3, 2019

General karthief said:
First off let me thank you for making me feel kinda dumb, I would not have even responded to this if you had give accurate info on what the car had for modifications, I'm not a blower guy.
Modifications are a very important point when looking for help on an internet forum where the helper can't lay hands on the car to see what has been done.
I'm usually not brassy in my responses but in this case I will agree you need to drive it till it breaks.

My bad lol I know that.

I blanked.

Damn thing is driving me crazy.

General karthief · Jul 3, 2019

I feel your pain dude.

Blown88GT · Jul 4, 2019

1. Are you blow-thru or draw-thru on the maf?
2. If blow-thru, the blower is always adding air, unless your BOV is 100%. I have blow-thru & BOV is about 50%.
3. 650 rpm with a blower & a cam is impossible with the factory ECU. I can't even go that low with a Megasquirt. It's likes 850 rpm.

Mrg2783 · Jul 5, 2019

Blown88GT said:
1. Are you blow-thru or draw-thru on the maf?
2. If blow-thru, the blower is always adding air, unless your BOV is 100%. I have blow-thru & BOV is about 50%.
3. 650 rpm with a blower & a cam is impossible with the factory ECU. I can't even go that low with a Megasquirt. It's likes 850 rpm.

Its a pull through MAF in the fender well

santos · Jul 5, 2019

on a side note, where did you get those black needles for the speedo gages??? looks awesome

Mrg2783 · Jul 5, 2019

santos said:
on a side note, where did you get those black needles for the speedo gages??? looks awesome

Unfortunately I dont know on that one. This cluster was bought back in 1996 by the original owner.

jrichker · Jul 5, 2019

Blown88GT said:
1. Are you blow-thru or draw-thru on the maf?
2. If blow-thru, the blower is always adding air, unless your BOV is 100%. I have blow-thru & BOV is about 50%.
3. 650 rpm with a blower & a cam is impossible with the factory ECU. I can't even go that low with a Megasquirt. It's likes 850 rpm.

Are you telling me that a centrifugal blower makes boost at idle speeds? I don't think so...

Blown88GT · Jul 5, 2019

jrichker said:
Are you telling me that a centrifugal blower makes boost at idle speeds? I don't think so...

No. You are confusing boost with flow.
Volumetric efficiency is around 100% due to decreased pumping losses. At low load cruise, it's higher than 100%.

General karthief · Jul 5, 2019

How can you confuse boost with flow?
she sells insurance!

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