Engine Idle issue - Possible Vac leak - canister purge valve?

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After double checking every possible Vacuum source / component, I was able to narrow it down to the purge valve being stuck open allowing a constant vac leak during idle. I replaced with a new motorcraft valve and that did the trick stopping the constant vac at idle. I also inspected and opened all the 10 pin pins for better contact. I thought now the idle should calm down and stop the surging but it didn't. Idle was still at about 950 and still surge slooowly up to 1300 when hitting the throttle. If you hit it again, it would calm back down to 950 rpm..
I checked the vacuum level at idle. It's a steady 20 and 22 if I hold the rpms at 1500.

I wanted to perform another base idle reset. This time pulling the spout as you guys suggested. Timing was and is right at 10 btdc.
Well I'm excited to say that pulling the spout did the trick!! :rock:Before doing an idle reset with the spout in, I could never the base idle down to 600 rpm using the throttle plate screw / IAC pulled. the lowest I could get it was 750.. Now with pulling the Spout?!! I actually had to turn UP the screw to keep it running.. haha and I was now able to dial it in to 600 / 625! After doing the entire reset with your suggestion, I now have her idling at 750 range and no surge! :cheers:

I know there's a ton of write ups about how to perform a base idle reset, but I every list I found, there's always something different and a lot of them don't say to pull the spout. I would like the opportunity to present my own BASE IDLE RESET PROCEDURE that I pieced together from you tube, forums, posts and ford bulletins. I'm sure everyone has their own way of doing an idle reset but I found this procedure to work for me, curing my high idle and slight surge hanging idle. Just make sure your timing is correct (Factory spec is 10° btdc) and you do not not not have any vac leaks before performing an idle reset for the best possible outcome.

1. Warm Engine to temp then turn off
2. Disconnect Battery for 10 minutes
3. Disconnect IAC connection, TPS connection and pull the SPOUT

This will remove all ECU connections controlling idle.
4. Reconnect the battery and start engine.
5. Manually set idle between 600 - 650 rpms (600-625 preferred) using the throttle plate screw located under the Throttle Body.

If idle is too low and doesn't stay running, turn the idle screw clockwise a quarter turn and try again.
6. Once base rpms are achieved, turn off engine and reconnect IAC, TPS and SPOUT.
7. With KOEO (key on engine off) set the TPS voltage between .90-.95 volts.

You achieve this by probing the green wire as positive and the black wire as negative. for the most accurate reading, use the black wire ONLY as ground!
Loosen the TPS slightly and now test between the green and black wire using a digital multimeter.
Turn the TPS until you're dialed in between .90-.95 volts.
You may need to remove the TPS and elongate the holes slightly to get enough movement to dial in.
8. Start engine and idle for 2 minutes without any accessories on. Time it!
9. Turn off engine for 2 minutes. Time it!
10. Start engine again and idle for another 2 minutes but this round with all accessories on. Time it!

(headlights, hazards, Hvac blower) anything to draw current and create a load.
11. Turn off engine.

You have completed your base idle reset procedure!

You should notice your idle is now dialed in around 750 rpm.

Thanks again everyone. I hope this helps someone!
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you didn't learn nothin from me, I just regurgitate stuff others have posted to help members with problems and maybe a little googlefu thrown in just to make me sound like I know what I'm posting.
could u help me with a vacuum leak also I took out my smog system and this is my first mustang I took the tad and tab vacuum lines off and to the EGR I hooked up one silonoid with the green and red and tried to run them to the back of intake and EGR I've looked at the diagram and I'm confused on where to plug stuff
could u help me with a vacuum leak also I took out my smog system and this is my first mustang I took the tad and tab vacuum lines off and to the EGR I hooked up one silonoid with the green and red and tried to run them to the back of intake and EGR I've looked at the diagram and I'm confused on where to plug stuff
Do you have a thread started with this problem?

I know this has been discussed all over this site with some really good detailed checklists to troubleshoot with too.

I have a possible vac leak. I've done base idle reset which works "ok" but I cant seem to get her under 950 - 1000 RPM. At full warmup it sits at 950 - 1000. Once you hit the throttle, it comes down to idle but then starts to rise up to 1300 to 1500 and a little hunting. I hit the throttle again, sometimes it takes 3 jabs but the idle will drop quickly back down to 950-1000 and stay there until you tap the gas and it starts all over again.

When I disconnect the IAC, idle does drop but I cant get it to 600-650 base rpms using the TB screw. Even when turned all the way out it hovers at 750. There is a small hole on the butterfly which is supposed to be there, but when I plug it up with my finger, idle goes down what it should.. This is telling me I have a vac leak somewhere, no? I have performed a process of elimination going around and capping off one thing at a time. Capped off the brake booster at the tree to eliminate the BB. This didn't make a difference. Hvac, same thing. Cruise Control, same thing. Fuel pressure reg is new and new line, New EGR valve since there was a little leak with the diaphragm. This helped a little. two new IAC's. tested TPS, all good. TAB and TAD are new with new lines.

KOEO codes - 11 1 11
KOER codes - 11 1 11
CYL balance test - 9

The last thing I needed to check was the canister purge valve. I disconnected the line from the upper intake and applied hand vacuum to it. It would not hold Vac!! Yessss!
I disconnected the valve from the canister and re applied vac. Still would not hold vac and this is the original on the car. Now if I lightly "tap" the valve while applying vac, it seems to be better at holding so I just picked up a new Motorcraft one since they are suppose to be the best .
I applied vac to the new one to test and it doesn't hold vac!! whaaaat! with a slight tap it then works. I checked the ohms and its right in line. I even plugged it in and did a KOEO to energize the valve thinking this would close it and nothing.

My question is - does the engine need to run to energize the valve and signal it to closet to hold vac at idle? I know these valves are suppose to stay closed at idle and WOT and only open at cruising speed.

Just thinking also, when performing base idle reset with the IAC unplugged, are you also supposed to disconnect the SPOUT? I ask because I did not do that and some internet searches say to. I dunno.....

Thank you for all your help and time.
Hey man I feel like the
I would assume too that the valve would be closed when powered as to not allow fumes to enter the intake during idle or it would create a vacuum leak.

I applied 12 volts to both old and new valves and it doesn't matter. They both stay open and allow air to flow.

Just thinking out loud here. With engine running, when does the ECU "ground" the valve? and when grounded, does the valve open or close?
Perhaps the valve actually works in reverse, meaning when grounded, it closes the valve which would be most of the time. At cruising speeds the ground would be lifted and the valve would open..

I guess there is only one way to figure this out and eliminate a strange theory. :chin
the has to be naturally closed. Gets battery power and switched ground from pcm. I don’t want to sound like an idiot but is the vac pump you using operational. Only asking cuz I’ve been i a situation where the vacuum pump was toast. I believe it the purge operatates when vehicle is cruising.
A faulty purge valve should cause a richer condition. But mine does not work and…wiring is good…so it’s the valve and I have no issues. I have eliminated a lot tho. So less headaches.you need to get a manifold vacuum reading. Is it possible your IAT valve is stuck open? If it lowers to the point where it’s supposed to be then it’s your IAT. You can check you MAF sensor. See if it needs a cleaning and or replacement.
If you haven’t already inspected the salt n pepper shakers….I used a dentist pick (like dollar store quality) and opened up pins for better terminal tension. I’ve been burned before. Might also be a leak in the hvac system? Good luck man. Let us know what you find. Knowledge is power.
could u help me with a vacuum leak also I took out my smog system and this is my first mustang I took the tad and tab vacuum lines off and to the EGR I hooked up one silonoid with the green and red and tried to run them to the back of intake and EGR I've looked at the diagram and I'm confused on where to plug stuff

Thermactor Air System
Some review of how it works...

Revised 25 May 2019 to re-order paragraph sequence and add lean burn description for newer cars

The Thermactor air pump (smog pump) supplies air to the heads or catalytic converters. This air helps break down the excess HC (hydrocarbons) and CO (carbon monoxide). The air supplied to the catalytic converters helps create the catalytic reaction that changes the HC & CO into CO2 and water vapor. Catalytic converters on 5.0 Mustangs are designed to use the extra air provided by the smog pump. Without the extra air, the catalytic converters will clog and fail.

The Thermactor air pump draws air from an inlet filter in the front of the pump. The smog pump puts air into the heads when the engine is cold and then into the catalytic converters when it is warm. The air provided by the air pump serves to help consume any unburned hydrocarbons by supplying extra oxygen to the catalytic process. With a warm engine, the computer operates on closed loop mode, taking input from all the sensors.

The Thermactor control valves serve to direct the flow. The first valve, TAB (Thermactor Air Bypass) or AM1 valve) either dumps air to the atmosphere or passes it on to the second valve. The computer tells the Thermactor Air System to open the Bypass valve at WOT (wide open throttle) minimizing engine drag. This dumps the pump's output to the atmosphere, and reduces the parasitic drag caused by the smog pump to about 2-4 HP at WOT. The Bypass valve also opens during deceleration to reduce or prevent backfires.

The second valve, TAD (Thermactor Air Diverter valve or AM2 valve) directs it to the heads or the catalytic converters. Check valves located after the TAD solenoid prevent hot exhaust gases from damaging the Diverter control valve or air pump in case of a backfire.

Code 44 RH side air not functioning.
Code 94 LH side air not functioning.

How the O2 sensors affect the operation of the Thermactor Air System.
The computer uses the change in the O2 sensor readings to detect operation of the Thermactor control valves. When the dump valve opens, it reduces the O2 readings in the exhaust system. Then it closes the dump valve and the O2 readings increase. By toggling the dump valve (TAB), the computer tests for the 44/94 codes.

Failure mode is usually due to a clogged air crossover tube, where one or both sides of the tube clog with carbon. The air crossover tube mounts on the back of the cylinder heads and supplies air to each of the Thermactor air passages cast into the cylinder heads. When the heads do not get the proper air delivery, they set codes 44 & 94, depending on which passage is clogged. It is possible to get both 44 & 94, which would suggest that the air pump or control valves are not working correctly, or the crossover tube is full of carbon or missing.


Computer operation & control for the Thermactor Air System.
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.

One side of the any relay/actuator/solenoid in the engine compartment will be connected to a red wire that has 12-14 volts anytime the ignition switch is in the run position. The other side will have 12-14 volts when the relay/actuator/solenoid isn't turned on. Once the computer turns on the clamp side, the voltage on the computer side of the wire will drop down to 1 volt or less.

In order to test the TAD/TAB solenoids, you need to ground the white/red wire on the TAB solenoid or the light green/black wire on the TAD solenoid. The TAB and TAD solenoid are located on the passenger side shock strut tower. Uneducated owners sometimes remove them to get more HP. This does not work, it just causes 81 & 82 codes.

For 94-95 cars: the colors are different. The White/Red wire (TAB control) is White/Orange (Pin 31 on the PCM). The Green/Black wire (TAD control) should be Brown (pin 34 at the PCM). Thanks to HISSIN50 for this tip.

Testing the system:

To test the computer, you can use a test light across the TAB or TAD wiring connectors and dump the codes. When you dump the codes, the computer does a self test that toggles every relay/actuator/solenoid on and off. When this happens, the test light will flicker.

Disconnect the big hose from smog pump: with the engine running you should feel air output. Reconnect the smog pump hose & apply vacuum to the first vacuum controlled valve: Its purpose is to either dump the pump's output to the atmosphere or pass it to the next valve.

The next vacuum controlled valve directs the air to either the cylinder heads when the engine is cold or to the catalytic converter when the engine is warm. Disconnect the big hoses from the back side of the vacuum controlled valve and start the engine. Apply vacuum to the valve and see if the airflow changes from one hose to the next.

The two electrical controlled vacuum valves mounted on the rear of the passenger side wheel well turn the vacuum on & off under computer control. Check to see that both valves have +12 volts on the red wire. Then ground the white/red wire and the first solenoid should open and pass vacuum. Do the same thing to the light green/black wire on the second solenoid and it should open and pass vacuum.

Remember that the computer does not source power for any actuator or relay, but provides the ground necessary to complete the circuit. That means one side of the circuit will always be hot, and the other side will go to ground or below 1 volt as the computer switches on that circuit.

The computer provides the ground to complete the circuit to power the solenoid valve that turns the
vacuum on or off. The computer is located under the passenger side kick panel. Remove the kick panel & the cover over the computer wiring connector pins. Check Pin 38 Solenoid valve #1 that provides vacuum to the first Thermactor control valve for a switch from 12-14 volts to 1 volt or less. Do the same with pin 32 solenoid valve #2 that provides vacuum to the second Thermactor control valve. Starting the engine with the computer jumpered to self test mode will cause all the actuators to toggle on and off. If after doing this and you see no switching of the voltage on and off, you can start testing the wiring for shorts to ground and broken wiring. An Ohm check to ground with the computer connector disconnected & the solenoid valves disconnected should show open circuit between the pin 32 and ground and again on pin 38 and ground. In like manner, there should be less than 1 ohm between pin 32 and solenoid valve #2 and pin 38 & Solenoid valve #1.

If after checking the resistance of the wiring & you are sure that there are no wiring faults, start looking at the solenoid valves. If you disconnect them, you can jumper power & ground to them to verify operation. Power & ground supplied should turn on the vacuum flow, remove either one and the vacuum should stop flowing.

Typical resistance of the solenoid valves is in the range of 20-70 Ohms.

What happens when there is no extra air from the smog pump...
As engines age, the quality of tune decreases and wear causes them to burn oil. We have all seem cars that go down the road puffing blue or black smoke from the tailpipe. Oil consumption and poor tune increase the amount of HC the oxidation catalyst has to deal with. The excess HC that the converters cannot oxidize due to lack of extra air becomes a crusty coating inside the honeycomb structure. This effectively reduces the size of the honeycomb passageways and builds up thicker over time and mileage. Continuous usage under such conditions will cause the converter to fail and clog. The extra air provided by the Thermactor Air System (smog pump) is essential for the oxidation process. It oxidizes the added HC from oil consumption and poor tune and keeps the HC levels within acceptable limits.
b]Newer catalytic converters do not use the Thermactor Air System (smog pump) because they are designed to work with an improved computer system that runs leaner and cleaner [/b]
They add an extra set of O2 sensors after the catalytic converters to monitor the oxygen and HC levels. Using this additional information, the improved computer system monitors the health and efficiency of the catalytic converters. If the computer cannot compensate for the added load of emissions due to wear and poor tune, the catalytic converters will eventually fail and clog. The periodic checks (smog inspections) are supposed to help owners keep track of problems and get them repaired. Use them on an 86-95 Mustang and you will slowly kill them with the pollutants that they are not designed to deal with.

Theory of operation:
Catalytic converters consist of two different types of catalysts: Reduction and Oxidation.
The Reduction catalyst is the first converter in a 5.0 Mustang, and the Oxidation converter is the second converter. The Oxidation converter uses the extra air from the smog pump to burn the excess HC. Aftermarket converters that use the smog pump often combine both types of catalysts in one housing. Since all catalytic reactions depend on heat to happen, catalytic converters do not work as efficiently with long tube headers. The extra length of the long tubes reduces the heat available to operate the O2 sensors and the catalytic converters. That will cause emissions problems, and reduce the chances of passing an actual smog test.

Now for the Chemistry...
"The reduction catalyst is the first stage of the catalytic converter. It uses platinum and rhodium to help reduce the NOx emissions. When an NO or NO2 molecule contacts the catalyst, the catalyst rips the nitrogen atom out of the molecule and holds on to it, freeing the oxygen in the form of O2. The nitrogen atoms bond with other nitrogen atoms that are also stuck to the catalyst, forming N2. For example:

2NO => N2 + O2 or 2NO2 => N2 + 2O2

The oxidation catalyst is the second stage of the catalytic converter. It reduces the unburned hydrocarbons and carbon monoxide by burning (oxidizing) them over a platinum and palladium catalyst. This catalyst aids the reaction of the CO and hydrocarbons with the remaining oxygen in the exhaust gas. The "lean burn" technology of newer cars means there is more O2 for the oxidation process to work with.

For example:

2CO + O2 => 2CO2

There are two main types of structures used in catalytic converters -- honeycomb and ceramic beads. Most cars today use a honeycomb structure." Quote courtesy of How Stuff Works (HowStuffWorks "Catalysts")

Code 45 & 46 are very uncommon, this is the first time in 20+ years here at Stangnet that I have seen them posted.

The TAD solenoid and its plumbing are the probable source since it appears that the TAD solenoid is stuck open during self-test. Check for vacuum at the Diverter valve when running the self-test routine.

“C:\Users\Joe\Documents\Stangnet\Parts orders\89 Mustang\smog pump control valves location.gif”

You guys with idle/stall problems could save a lot of time chasing your tails if you would go through the Surging Idle Checklist. Over 50 different people contributed information to it. The first two posts have all the fixes, and steps through the how to find and fix your idle problems without spending a lot of time and money. It includes how to dump the computer codes quickly and simply as one of the first steps. I continue to update it as more people post fixes or ask questions. You can post questions to that sticky and have your name and idle problem recognized. The guys with original problems and fixes get their posts added to the main fix. :D
I have a new issue now I have something leaking from the bellhousing and just replaced the valve cover gaskets and upper intake I can see the heads need them and I have the gaskets but do the heads come right off ,is the head gaskets right there also if I showed u under the car the motor is gross and the frame is rust free lol let me know what u think