If it's not the IAC, then...

[DEMonte1997]

1999 Grand Am. 3400 engine.

Car randomly idles high. Start the car, idle will begin at 2.5Krpms and climb past 3K. I thought it was the idle air control valve because I could get the condition to go away by pumping the gas pedal before starting the car. Now the IAC has been replaced and it's still idling high. Pumping the gas pedal seems to alleviate the problem for a short period of time. The dealer has told me that it could be the throttle position sensor, but I'm not all about having them replace something that's not broken.

Any ideas?

Thanks!

[sunrunner_pei]

I'd say either a bad TPS sensor or a vacuum leak.

[DEMonte1997]

Thanks Shawn. I'm thinking about just replacing the TPS and calling it a day. I can't see it being a vacuum line leak b/c the condition somehow goes away whenever you pump the gas pedal before starting the car. It's also very intermittent.. one day it idles high, the next day it doesn't. When it idles high, the shift points for the tranny seem off. The car doesn't hold gear as well and it seems a little starved for power.

I'm thinking it has to be related to the TPS or more exactly the IAC. Sucks that I already replaced the IAC :( .. I was really hoping that it was the problem.

If anyone else has thoughts about this, please feel free to advise. I'm going to probably just order a TPS and put it in this weekend.

[cocobob]

What does the scan tool say. This might help you to troubleshoot more precisely.

[DEMonte1997]

Since the car is my girlfriend's and she lives in RI and I live in VT, my hands are kinda tied. The car is at a dealership now. According to them, the car didn't seem that far off (according to their diagnostic scanner). The thing is that I think my girlfriend pumped the gas pedal before she brought the car there, SO it's not acting up currently. Something about pumping the gas is disengaging the throttle so it doesn't idle high..

The dealership also said that they think it's the TPS, but I've heard totally conflicting thoughts. Some people have said that it cannot be the TPS if the car does this at idle. Other's have said it can. I don't really trust the dealership techies farther than I could throw one because they haven't been able to diagnose ANYTHING on her car correctly.

My girlfriend is probably going to drive up to VT this weekend to see me.. soooo .. if the car is still acting up, I'm going to have to work on it. That's why I'm polling everyone here. :lol: :lol:

Could the throttle linkage be sticking? How would I go about fixing that?

[4kQuad]

If it's not the TPS, it could just be dirty crap build up inside the throttle body where the butterfly is. The TPS moves it or moves with it.

I'm thinking the pumping of the gas moves the butterfly back and forth kind of freeing it up till the next time the whole motor gets cold again. When it's cold the build up get stiff again making the butterfly stick causing problems in the idle RPM.

To find the butterfly take the air hose off the end of the throttle body, look up inside the throttle body. Either move the throttle linkage or have someone step on the gas so yoyu can see the butterfly move. it's the big metal flap.

[sunrunner_pei]

Yeah, like 4kQuad mentioned, could be the TB sticking. A simple thing to try would be some TB cleaner spray.

[DEMonte1997]

Thanks for the suggestions guys. I'll report back at the end of the weekend.

This situation is compounded b/c my car, 1997 Monte, lost its tranny at 40K miles. So it's been in the shop for the past 2 weeks. Having two GM cars working as poorly as this at the same time is really making my head hurt.

[sunrunner_pei]

I got your PM... Here is the TPS replacement instructions in PDF format. :)

Are there any DTCs set?

[sunrunner_pei]

DTC P0507 Idle Speed High

From Document # 304017:

The PCM controls engine idle speed by adjusting the position of the Idle Air Control (IAC) motor pintle. The IAC is a bi-directional motor driven by two coils. The PCM applies current to the IAC coils in steps (counts) to extend the IAC pintle into a passage in the throttle body to decrease air flow. The PCM reverses the current to retract the pintle, increasing air flow. This method allows highly accurate control of idle speed and quick response to changes in engine load. If the PCM detects a condition where too high of an idle speed is present and the PCM is unable to adjust idle speed by decreasing the IAC counts, DTC P0507 will set indicating a problem with the idle control system.



Conditions for Setting the DTC

No active EVAP, misfire, EGR, TP sensor, VSS, ECT sensor, MAP sensor, IAT sensor, Fuel Trim, injector circuit, CKP sensor, MAF sensor DTCs active.
Engine Coolant Temperature is above 70°C (122°F).
The engine has been running for at least 2 minutes.
System voltage is between 9-18 volts.
Vehicle Speed is less than 3 MPH.
Intake Air Temperature is above -18°C (0°F).
The TP Sensor is less than 1.5 percent
Engine Speed is 175-300 RPM higher than Desired Idle.
BARO above 65 kPa.
Engine run time is greater than 2 minutes.
All the above conditions have been met for a minimum of 15 seconds.


Check for the following conditions:

Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage.
Vacuum leak. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, faulty or incorrectly installed crankcase ventilation valve, leaks at intake manifold, etc.
Throttle body. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.

[sunrunner_pei]

Engine Data Sensors Schematic:

[DEMonte1997]

OMG Shawn, I feel like it is my birthday! Thank-you so much for the extra posts. This site is simply amazing :D. These will surely make my job easier when I take a crack at solving this problem.

I already replaced the IAC valve a couple weekends back and that didn't help. The car hasn't thrown any codes for this-oddly enough. This weekend I plan on giving the throttle body a thorough cleaning and checking that the IAC was installed correctly. I will probably end up replacing the TPS-since it is only $30. Lastly, I will do an idle re-learn. I'll probably go ahead and clean the K&N air filter that I installed a few months ago too.

Overall, my girlfriend's car should be pretty happy after all this is done.

I'll let you all know how it turns out next week.

Thanks again!

[sunrunner_pei]

If you're going to work on the IAC valve, this document should help you:

[sunrunner_pei]

And some more help from document #311336...


Check for the following conditions:

Poor connection at PCM or IAC motor. Inspect harness connectors for backed out terminals, improper mating, broken locks, improperly formed or damaged terminals, and poor terminal to wire connection.
Damaged harness. Inspect the wiring harness for damage.
Restricted air intake system. Check for a possible collapsed air intake duct, restricted air filter element, or foreign objects blocking the air intake system.
Throttle body. Check for objects blocking the IAC passage or throttle bore, excessive deposits in the IAC passage and on the IAC pintle, and excessive deposits in the throttle bore and on the throttle plate. Check for a sticking throttle plate. Also inspect the IAC passage for deposits or objects which will not allow the IAC pintle to fully extend.
Vacuum leak. Check for a condition that causes a vacuum leak, such as disconnected or damaged hoses, leaks at EGR valve and EGR pipe to intake manifold, leaks at throttle body, faulty or incorrectly installed PCV valve, leaks at intake manifold brake booster hose disconnected, etc.

[sunrunner_pei]

If the IAC valve has been in service: DO NOT push or pull on the IAC valve pintle. The force required to move the pintle may damage the threads on the worm drive. Also, DO NOT soak the IAC valve in any liquid cleaner or solvent, as damage may result.

[DEMonte1997]

It's fixed! :D

Turned out to be the TPS.

Thanks to everyone who listened to my ramblings and gave advice!

[HeyDace]

And you didn't trust the Dealer "Techies", of which I am one. LOL.
Glad it worked out for you.

[DEMonte1997]

Sorry dude, I trusted you just not for $200. I mean.. the part is only $30. :)