High Idle - anyone...? WMBurns??

[GDawg]

Okay guys, on Saturday I noticed my idle was a little high. The idle ran high(er) on warm up and then after dropping still high(er) after warm up than normal. So on Sunday I'm going to Lowes and at a left hand turning red light my idle jumped to 4000rpm at curb idle. The engine was screaming. No check engine light YET. I actually had to release the clutch a bit to slow the engine down. I figured better to have to replace the clutch than the engine. So the light turns green and I muscle the car back home. On the way home came on the check engine light. So I stop at an AutoZone on the way home and retrieve a P1506 DTC (IAC overlimit or vacuum leak.) I know what a vacuum leak feels like in my car and I'm pretty sure it's not that (Idle is high and steady not jumping all over the place. It's not bucking.) Added note: It was REALLY cold that day and now it's still staying cold but not always below 32*. So, not really completely knowing what to do, I buy MAF cleaner and cleaned my IAC. The idle dropped but is still about 1000 rpms too high at pre-warm up and warm up. So I go buy a new IAC. The same... warmed up I'm idling at 1700 rpm and not ~700 rpm.

I'm going to clean the MAF next. I don't think it's the PCV or anything else EXCEPT maybe the TPS. Seems like the TPS is not seeing where the (TB) butterfly (not a good description) blade (valve?) is really at.

You know what I mean, right? Just trying to get all the terms correct.

I have reset the computer overnight and gave it time to relearn.

I can probably drive the car 10 miles to my school and have them run the Solice on it but I hate to drive it that far with this condition.

So...

School me brothers! And hopefully WMBurns will chime in cause he's good at this stuff.

TIA

:SNSign:

 

[Rickyll7]

Have you tried unplugging the IAC valve while the engine is idling? Did you buy a Ford, OEM IAC valve?

 

[fast97gt]

Did you disconnect the battery while performing the work? If not the computer won't recognize the new part(s). Also do double check the vacuum lines, and no reseting the computer is not the same as disconnecting the battery.
Posted via Mobile Device

 

[GDawg]

Did you disconnect the battery while performing the work? If not the computer won't recognize the new part(s). Also do double check the vacuum lines, and no reseting the computer is not the same as disconnecting the battery.
Posted via Mobile Device

After cleaning the IAC I disconnected the battery over night. After installing the new one I disconnected the battery for two hours. That black knob on the IAC... what does it do and is it adjustable? The IAC I bought was from AutoZone and it's a Duralast. I may be able to take it back since it's only been on the car two days with no miles on it and only 20 minutes of run time at idle.

 

[Rickyll7]

After cleaning the IAC I disconnected the battery over night. After installing the new one I disconnected the battery for two hours. That black knob on the IAC... what does it do and is it adjustable? The IAC I bought was from AutoZone and it's a Duralast. I may be able to take it back since it's only been on the car two days with no miles on it and only 20 minutes of run time at idle.

The parts guy at my local Ford dealership told me the black knob looking thing is an atmosphere pressure reference or something. I don't think there is anything to adjust there.

 

[fast97gt]

After cleaning the IAC I disconnected the battery over night. After installing the new one I disconnected the battery for two hours. That black knob on the IAC... what does it do and is it adjustable? The IAC I bought was from AutoZone and it's a Duralast. I may be able to take it back since it's only been on the car two days with no miles on it and only 20 minutes of run time at idle.

but did you disconnect the battery while you put the on the new iac, if not disconnect the battery, unplug the iac, then let it sit for 20mins. then plug it back in, cinnect the the battery, ive done several times and has worked everytime. the black knob is a black knob, no but anyway, if the new one from autozone didnt fix it (i have a duracrap on my car and its fine) then search else where, like a vacuum leak... on my 2000gt we swapped the crappy intake for the good one with aluminum x-over i used the supplied gasket (paper) which was the wrong one, it shouldve been plastic with the silicone inlay. now my point, the engine raced constently until i figured out it was a vacuum leak from the defective gasket that came with the intake. so check and double check your vacuum lines, especially the 90 degree connector on the driverside valve cover.

 

[GDawg]

but did you disconnect the battery while you put the on the new iac, if not disconnect the battery, unplug the iac, then let it sit for 20mins. then plug it back in, cinnect the the battery, ive done several times and has worked everytime. the black knob is a black knob, no but anyway, if the new one from autozone didnt fix it (i have a duracrap on my car and its fine) then search else where, like a vacuum leak... on my 2000gt we swapped the crappy intake for the good one with aluminum x-over i used the supplied gasket (paper) which was the wrong one, it shouldve been plastic with the silicone inlay. now my point, the engine raced constently until i figured out it was a vacuum leak from the defective gasket that came with the intake. so check and double check your vacuum lines, especially the 90 degree connector on the driverside valve cover.

I'll try that today. Thanks for the info.

 

[wmburns]

IAC pinpoint test KE20

Regarding the posts about what order to do the work, I disagree. There is NOT a direct 2 way communication loop between the IAC itself and the PCM. Makes no difference when the IAC is replaced as long as the battery is disconnected somewhere in the process.

If the battery is not disconnected, there can be a delay as the PCM re-learns the idle trim values. The delay could be up to 15 minutes idle time (not days/weeks as others have claimed). In any case, there is a procedure that should be followed regardless. Run the car at idle in park/neutral AC off for at least one FULL minute. Turn the AC on and allow the engine to idle for at least one FULL minute. Do not touch anything during the full minute idle.

As far as the far as the black knob is concerned, it is an atmospheric vent.

Really some of the stuff posted sounds almost like voodoo. Disconnecting the battery for 15 minutes should be more than enough. But here is a trick for those out there that think the battery needs to be disconnected for extended periods of time. Disconnect the negative cable from the battery. Jumper the loose negative cable to the positive cable. This will drain away any residual charge in the PCM and the air bag systems.

DTC P1505 is pinpoint test KE20. The first item listed is check for VACUUM LEAKS. The next item listed is stuck open evaporative purge solenoid. Next is the IAC itself.

Since it is so easy, let’s start out with a basic IAC test. Disconnect the IAC electrical connection (engine running at idle). If the car immediately stops (or slows down), the IAC is basically working. Otherwise, there is a vacuum leak, evaporative purge solenoid stuck open, bad IAC or the wiring to the IAC is bad.

Check the throttle return spring. Is the butterfly valve closing all the way? Has the TB stop screw been adjusted? If it has, this could cause your problem. The TB must close all the way. The system is designed so that virtually all of the idle air is via the IAC.

The Ford service CD states that a bad/noisy TPS or loose throttle plates can cause a high idle.

Do you have access to an ODB2 scan tool to monitor IAC percent? Monitor with the AC on/off. Turn on/off head lights and observe to see if the percent changes. Post the results.

>>>from Ford service manual pinpoint test KE20
KE20 DTC P1506: CHECK FOR VACUUM LEAKS
Key on, engine running.
With the engine at idle, listen for vacuum leaks.
Inspect the entire intake air system from the mass air flow (MAF) sensor to the intake manifold for damage or leaks such as:
Cracked or punctured intake air tube.
Loose or cracked IAC air tubes.
Loose intake air tube at the air cleaner housing or throttle body.
IAC valve or gasket seal.
Intake manifold assembly or gasket seal.
EGR valve gasket seal.
Vacuum supply connectors and hose.
PCV valve, connectors and hose.
Are any leaks detected in the above areas?

(yes)KEY OFF. REPAIR as necessary. (no)KEY OFF. GO to KE21 .

KE21 CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE
Disconnect hoses at EVAP canister purge valve (or VMV).
Connect a hand vacuum pump at the fuel vapor port to EVAP canister at the EVAP canister purge valve (or VMV).
Apply 53 kPa (16 in-Hg) of vacuum to EVAP canister purge valve (or VMV).

Does the EVAP canister purge valve (or VMV) hold vacuum for 20 seconds?
(yes)RECONNECT hoses. GO to KE22 . (no)REPLACE EVAP canister purge valve.

KE22 CHECK IAC VALVE FOR PROPER FUNCTION
Key on, engine running.
Bring engine to normal operating temperature.
Transmission in PARK or NEUTRAL.
Disconnect IAC valve.
Does the rpm drop or engine stall?
(yes)KEY OFF. GO to KE23 . (no)KEY OFF. INSPECT throttle body for damage. REPAIR as necessary. If OK, REPLACE IAC valve. RESET Keep Alive Random Access Memory (RAM). (REFER to Section 2, Powertrain Control Module (PCM) Reset .)

KE23 CHECK IAC CIRCUIT FOR SHORT TO GND IN HARNESS
Note: Refer to the PCM connector pin numbers in the beginning of this Pinpoint Test.

Disconnect scan tool from DLC.
Disconnect PCM.
Measure resistance between IAC circuit at the PCM harness connector and battery negative post.
Is each resistance greater than 10,000 ohms?

(yes)For fast idle symptom currently present:

REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ).

All others:
RESTORE vehicle. GO to KE30.
(no)REPAIR short circuit.

KE30 CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT
Scan tool connected.
Key on, engine running.
Access IAC PID and RPM PIDs.
With engine at normal operating temperature, accessories off and at idle, the IAC duty cycle must be between 20% and 45%.
Observe the PIDs for an indication of a fault while completing the following at idle:
Lightly tap on IAC valve and wiggle harness connector to simulate road shock.
Grasp the vehicle harness closest to the IAC valve. Shake and bend a small section of the harness from the IAC to the dash panel and from the dash panel to the PCM.
Do the IAC or RPM PIDs suddenly change in value indicating a fault?
Yes No
(yes) ISOLATE fault and REPAIR as necessary.

(no)For idle quality, starting or stalling symptoms currently present:
REPLACE IAC valve.
All others:
Unable to duplicate or identify fault at this time. GO to Z1 .

 

[Rickyll7]

You're the man, WMBurns.

 

[fast97gt]

Regarding the posts about what order to do the work, I disagree. There is NOT a direct 2 way communication loop between the IAC itself and the PCM. Makes no difference when the IAC is replaced as long as the battery is disconnected somewhere in the process.

If the battery is not disconnected, there can be a delay as the PCM re-learns the idle trim values. The delay would be in terms of minutes (not days/weeks as others have claimed). In any case, there is a procedure that should be followed regardless. Run the car at idle in park/neutral AC off for at least one FULL minute. Turn the AC on and allow the engine to idle for at least one FULL minute. Do not touch anything during the full minute idle.

In fact, the case could be made for an IAC repair (only) to NOT disconnect the battery but go straight to the idle re-learn procedure. Then the PCM will not have to re-learn all of the other settings.

As far as the far as the black knob is concerned, it is an atmospheric vent.

Really some of the stuff posted sounds almost like voodoo. Disconnecting the battery for 15 minutes should be more than enough. But here is a trick for those out there that think the battery needs to be disconnected for extended periods of time. Disconnect the negative cable from the battery. Jumper the loose negative cable to the positive cable. This will drain away any residual charge in the PCM and the air bag systems.

DTC P1505 is pinpoint test KE20. The first item listed is check for VACUUM LEAKS. The next item listed is stuck open evaporative purge solenoid. Next is the IAC itself.

Since it is so easy, let’s start out with a basic IAC test. Disconnect the IAC electrical connection. If the car immediately stops, the IAC is basically working. If it continues to run, there is a vacuum leak, evaporative purge solenoid stuck open, bad IAC or the wiring to the IAC is bad.

Check the throttle return spring. Is the butterfly valve closing all the way? Has the TB stop screw been adjusted? If it has, this could cause your problem. The TB must close all the way. The system is designed so that virtually all of the idle air is via the IAC.

Do you have access to an ODB2 scan tool to monitor IAC percent? Monitor with the AC on/off. Turn on/off head lights and observe to see if the percent changes. Post the results.

>>>from Ford service manual pinpoint test KE20
KE20 DTC P1506: CHECK FOR VACUUM LEAKS
Key on, engine running.
With the engine at idle, listen for vacuum leaks.
Inspect the entire intake air system from the mass air flow (MAF) sensor to the intake manifold for damage or leaks such as:
Cracked or punctured intake air tube.
Loose or cracked IAC air tubes.
Loose intake air tube at the air cleaner housing or throttle body.
IAC valve or gasket seal.
Intake manifold assembly or gasket seal.
EGR valve gasket seal.
Vacuum supply connectors and hose.
PCV valve, connectors and hose.
Are any leaks detected in the above areas?

(yes)KEY OFF. REPAIR as necessary. (no)KEY OFF. GO to KE21 .

KE21 CHECK EVAP SYSTEM FOR A STUCK OPEN VALVE
Disconnect hoses at EVAP canister purge valve (or VMV).
Connect a hand vacuum pump at the fuel vapor port to EVAP canister at the EVAP canister purge valve (or VMV).
Apply 53 kPa (16 in-Hg) of vacuum to EVAP canister purge valve (or VMV).

Does the EVAP canister purge valve (or VMV) hold vacuum for 20 seconds?
(yes)RECONNECT hoses. GO to KE22 . (no)REPLACE EVAP canister purge valve.

KE22 CHECK IAC VALVE FOR PROPER FUNCTION
Key on, engine running.
Bring engine to normal operating temperature.
Transmission in PARK or NEUTRAL.
Disconnect IAC valve.
Does the rpm drop or engine stall?
(yes)KEY OFF. GO to KE23 . (no)KEY OFF. INSPECT throttle body for damage. REPAIR as necessary. If OK, REPLACE IAC valve. RESET Keep Alive Random Access Memory (RAM). (REFER to Section 2, Powertrain Control Module (PCM) Reset .)

KE23 CHECK IAC CIRCUIT FOR SHORT TO GND IN HARNESS
Note: Refer to the PCM connector pin numbers in the beginning of this Pinpoint Test.

Disconnect scan tool from DLC.
Disconnect PCM.
Measure resistance between IAC circuit at the PCM harness connector and battery negative post.
Is each resistance greater than 10,000 ohms?

(yes)For fast idle symptom currently present:

REPLACE PCM (refer to Section 2, Flash Electrically Erasable Programmable Read Only Memory (EEPROM) ).

All others:
RESTORE vehicle. GO to KE30.
(no)REPAIR short circuit.

KE30 CHECK IAC SYSTEM FOR INTERMITTENT OPEN OR SHORT
Scan tool connected.
Key on, engine running.
Access IAC PID and RPM PIDs.
With engine at normal operating temperature, accessories off and at idle, the IAC duty cycle must be between 20% and 45%.
Observe the PIDs for an indication of a fault while completing the following at idle:
Lightly tap on IAC valve and wiggle harness connector to simulate road shock.
Grasp the vehicle harness closest to the IAC valve. Shake and bend a small section of the harness from the IAC to the dash panel and from the dash panel to the PCM.
Do the IAC or RPM PIDs suddenly change in value indicating a fault?
Yes No
(yes) ISOLATE fault and REPAIR as necessary.

(no)For idle quality, starting or stalling symptoms currently present:
REPLACE IAC valve.
All others:
Unable to duplicate or identify fault at this time. GO to Z1 .

riddle me this then batman, why when i replaced the iac in 97gt back in april i only unplugged the iac and never diconnected the battery, my high idle problem persisted. then i disconnected the battery, unplugged the iac, let the car sit for ~15mins the average time it takes to replace an iac, then plugged the iac back up, then connected the battery in that order and it works perfectly. so thats why i replied with that answer

 

[wmburns]

riddle me this then batman, why when i replaced the iac in 97gt back in april i only unplugged the iac and never diconnected the battery, my high idle problem persisted. then i disconnected the battery, unplugged the iac, let the car sit for ~15mins the average time it takes to replace an iac, then plugged the iac back up, then connected the battery in that order and it works perfectly. so thats why i replied with that answer

How long did you let it idle after doing the IAC repair? Perhaps it did not run long enough for the PCM to re-learn the trim settings on its own. Suspect that if the IAC % was monitored, you would see the PCM steadily trim the number as the PCM attempts to adjust the idle.

I contend that in your case, it was disconnecting the battery that did the trick. Disconnecting/reconnecting the IAC did nothing.

Good work Robin (vacuum leak via the gasket).

All kidding aside, today's cars are certainly complicated things. In many respects you have to be a computer programmer in order to work on them (please don't ask me what I do for a living). I hope I didn't offend.

 

[GDawg]

How long did you let it idle after doing the IAC repair? Perhaps it did not run long enough for the PCM to re-learn the trim settings on its own.

I contend that in your case, it was disconnecting the battery that did the trick. Disconnecting/reconnecting the IAC did nothing.

Good work Robin.

All kidding aside, today's cars are certainly complicated things. In many respects you have to be a computer programmer in order to work on them (please don't ask me what I do for a living). I hope I didn't offend.

Funny you should say that... I AM a computer programmer that's been unemployed for two years so now I'm in school for automotive...

 

[wmburns]

Bad TPS can cause high idle

I have done some additional reading and have found some interesting things.

First, please read the excerpt below. It indicates that a High idle problem could be caused by a bad/noisy TPS.

Next, I was wrong about how the PCM computes Idle trim. Apparently the method is different between the 1996 I once owned and the later models 1999+s. For the later models it may take up to 15 minutes of idling with the brake on for the PCM to re-learn the idle trim values. So reseting the PCM via battery disconnect is a good idea.

Hats off to fast97gt. However, I still stand by my comments regarding the two way communication between the IAC and PCM. Disconnecting the IAC is not needed to reset after repair. Disconnecting the battery does the trick.

>>>from 2002-2003 Ford Service CD.
Idle Speed Control Closed Throttle Determination
One of the fundamental criteria for entering rpm control is an indication of closed throttle. Throttle mode is always calculated to the lowest learned throttle position (TP) voltage seen since engine start. This lowest learned value is called "ratch," since the software acts like a one-way ratch. The ratch value (voltage) is displayed as the TPREL PID. The ratch value is relearned after every engine start. Ratch will learn the lowest, steady TP voltage seen after the engine starts. In some cases, ratch can learn higher values of TP. The time to learn the higher values is significantly longer than the time to learn the lower values. The brakes must also be applied to learn the longer values.

All PCM functions are done using this ratch voltage, including idle speed control. The PCM goes into closed throttle mode when the TP voltage is at the ratch (TPREL PID) value. Increase in TP voltage, normally less than 0.05 volts, will put the PCM in part throttle mode. Throttle mode can be viewed by looking at the TP MODE PID. With the throttle closed, the PID must read C/T (closed throttle). Slightly corrupt values of ratch can prevent the PCM from entering closed throttle mode. An incorrect part throttle indication at idle will prevent entry into closed throttle rpm control, and could result in a high idle. Ratch can be corrupted by a throttle position sensor or circuit that "drops out" or is noisy, or by loose/worn throttle plates that close tight during a decel and spring back at a normal engine vacuum.

 

[GDawg]

I fired up the car. She still idles around 2200 cold and 1700 warm. I did the AC for over a minute, then the Heater. It shifted the idle a bit but not significantly.

I revved the engine to 4k and it slowly dropped to 2500 before it dropped quicker to 1700 rpms.

I pulled the electrical connection to the IAC and absolutely no change in the idle. I inspected my vacuum lines and really don't think it's that...

BUT...

I've got some coolant on the floor that wasn't there before I fired her up tonight. I can't see where it's coming from. I wonder if I don't have a coolant leak that is somehow affecting the computer readings to mess up my idle...?

 

[Frankenstang838]

but did you disconnect the battery while you put the on the new iac, if not disconnect the battery, unplug the iac, then let it sit for 20mins. then plug it back in, cinnect the the battery, ive done several times and has worked everytime. the black knob is a black knob, no but anyway, if the new one from autozone didnt fix it (i have a duracrap on my car and its fine) then search else where, like a vacuum leak... on my 2000gt we swapped the crappy intake for the good one with aluminum x-over i used the supplied gasket (paper) which was the wrong one, it shouldve been plastic with the silicone inlay. now my point, the engine raced constently until i figured out it was a vacuum leak from the defective gasket that came with the intake. so check and double check your vacuum lines, especially the 90 degree connector on the driverside valve cover.

im flirting with this idle and IAC issue right now too guys......glad this thread got posted. I replaced mine with a Borg Warner unit, and i idle at around 900 low and 1100 high. so im gonna check this stuff out tommrow. but on another note, i had to do the aluminum x intake swap and ever seince i've had a crappy idle, a slight nonrythymic miss, that gets super bad around 1000-rpm, my #4 cylinder running really lean (no O2 codes ever thrown). I've had to replace that plug 3 times now cause it gets toasted. I have been trying to remember if i messed up on my intake torque sequence, and i can't recall.....i've ordered new gaskets JIC the old ones got messed up, and im gonna rip everything back off and do it all over again this weekend. If anyone has another idea or fix for this issue....im all ears. Cause if the intake or gaskets isn't the problem.....im lookin at a burnt valve or so im told.

 

[wmburns]

I pulled the electrical connection to the IAC and absolutely no change in the idle. I inspected my vacuum lines and really don't think it's that......?

If pulling the electrical connector to the IAC doesn't slow/change the idle, there is a problem.

The effective IAC duty cycle should go to zero when the connector is pulled. If it doesn't the stepper motor is not running and changing the orifice size. Unless the IAC is actually modulating the flow of air, it can't be expected to control the idle speed.

Try this next. Pull the 1/2" vacuum line to the IAC and the electrical connector. With your hand feel for vacuum at the IAC. See if blocking the line lowers/kills the idle (may have to block both sides). What we are trying to determine is where the idle air is coming from (the IAC or somewhere else).

I really think you will end up replacing your IAC.

I also think the coolant issue is an added PIA (unless you find some electrical connector wet with coolant).

 

[walterbenedikte]

real novice's question

Just have my 1st stang as of yesterday, idle is high at times, have not yet re-trained it ... wanted to first basically check the IAC (voltage and verify shut-off when disconnected) and (it is painfull, I know) wanted to make sure this is the right disconnect:

(hope at least have correctly attached the pic, thanks from an italian (so far) alfa-enthusiast)

edited:

I tried, it worked (disconnecting IAC the engine went off) ... let's see how it performs driving ... after retraining the idle falls back to 1000 and after 2 seconds to approx. 650 ...

thanks for the thread!

 

[fast97gt]

thank you wmburns appoligy accepted, but i had tried letting the car run for 15-20mins because thats what i was told to do. then that didnt fix it, so i diconnected everything then connected and wahla, tahda. sorry i had to bost fo second. and you have "checked" your vacuum lines then the problem lies deeper. i would definitly check the tps, egr, etc.

 

[wmburns]

walterbenedikte, Great picture of the IAC electrical connector. That's it. Idle at about 650. Sounds right to me.

Note, the slow rev down on Manual Mustangs is how the car is designed. They all do it.

Fast97gt, the other important detail about the re-learn process is that new idle trim values are learned only when the car's speed is zero and your foot is on the brake. Therefore, just running at idle is not enough. Your foot needs to be on the brake.

Therefore, much easier to just disconnect the battery after the repair. Start with a clean slate.

GDawg last post reported no change when the IAC electrical connector removed. Highly likely the IAC stepper motor is not moving. Perhaps it is stuck at a high enough duty cycle to allow the motor to start and run.

Of course, GDawg hasn't yet ruled out a partially open butterfly valve. Nor has a stuck open Evaporative purge valve (VMV) been ruled out.

There is a possibility that the TB set screw was adjusted slightly open to compensate for a malfunctioning IAC. Now that the weather has cooled, too much dense air is getting through and thus the high idle. The PCM would normally command a lower IAC duty cycle. The IAC stepper motor would close and reduce the amount of air the engine is getting thus lowering the idle. If too much air is getting by the TB, the IAC duty cycle could go to zero and the motor would still run.

 

[wmburns]

IAC design changed 2001

OK. I have some information to add. My own 2000 GT has an occasional problem with slow idle. This seamed like a good opportunity to put all of this to the test. When I did the basic functionally test, the motor did not die. This was curious because the car drives OK except for an occasional dying when cold.

Off to do research. What I found was Ford changed the IAC in 2001. The atmospheric vent was removed.

So. For models with the vent, when the electrical connection to the IAC is removed, there is a series of springs/diaphragms that allow air to enter the TB via the vent. This is to allows the motor to start even with a totally bad IAC. This means that the motor may not die if the electrical connection is removed. However, there should be a change in RPM.

For models without the vent, there only source of idle air is the IAC itself. Therefore, the motor will die if the electrical is disconnected and the IAC is working. This also means the car will not start if the IAC is bad.

The other difference is the one without the vent can be cleaned. Do not clean the model with the vent.

My results, a new Auto Zone replacement IAC and have not had any problems since.

GDawg, for your purposes, it may help to block the vent with tape. This will help determine if air is entering the TB via some other path. If you think it would help, I would be glad to give you my old IAC. I think it works but is weak.