Confusing Idle Problem....to high.

[GaryFenza]

2003 Pontiac Grand Prix GT 3800 Series II 122K miles.

On a cold day like 25 degrees in the morning, and first start of day, the car seems to idle at 1500RPM's FOREVER, until i tap the gas pedal and then it goes down to normal operating temperature where it should be, because the car is warm at this point, but only if i tap the gas, if not will continue idling at 1500rpms. I replaced the IAC and cleaned the heck out of the spot where it seats to the throttle body. Im a little confused, and there are no codes or nothing.

[tblake]

did you check out the tps?

[GaryFenza]

well im confused as hell, tomarrow i am buying a TPS for it. I just replaced the IAC. could it be my imagination.....On a very cold morning how long does your car idle at 1500RPMs' until it returns to normal speed of like 800 or 900rpm's. Problem is......the engine is warm and it is still at 1500 on my car.

[tblake]

mine will idle high untill it is warm, then 800-900.

[CrazyHorst]

I would recommend looking at the PCV valve. It controls an unmetered air leak around the throttle blade with the intent of moving and ingesting internal blowby and the resulting oil-side vapors. If it is stuck in the WOT position an not in the closed-throttle/high-vacuum state then you will have the same net effect of opening the throttle blade more.

Also, keep in mind that the signal which changes the cold-idle is the engine coolant temp.

Based on the initial coolant temp at startup, the PCM selects an initial air-fuel ratio to start the engine (rich mixture ala choke) and this then times out back to closed loop operation.

Since you've already been thru the IAC, I'd also say another possibility is to look at changing the engine coolant temp sensor.

[tblake]

Originally Posted by CrazyHorst

Since you've already been thru the IAC, I'd also say another possibility is to look at changing the engine coolant temp sensor.

Good point, but the same sensor is used for the guage and the PCM. If there was a problem with it, He would notice the guage not working or the PCM would trip a DTC.

Maybe the t-stat is sticking open, or the car is low on coolant... Causing longer warm up times.