Random very high / fast idle speed...

[PCweber]

About every 3 times my daughter drives her 97 GT she says it idles at around 2500 RPMs. I saw it doing it today myself and checked the throttle plate was returning to the stop and it was. I changed the IAC with a know good one off my son's 98 GT a few weeks ago. Also swapped the TPS & MAF sensors. I had put a new upper intake on the 97 last winter so I am not thinking that it could have an upper intake vacuum leak. Any common items I can check or ways to test for vacuum leaks?

 

[cerick08GP]

I would check the fuel injector O-rings.

 

[Liquifire]

take some carb cleaner and start spraying around the intake manifold area, and also around any vacuum lines/connections with the car running. If your car idles pick up in any one area, you have found the leak. Spray liberally....

 

[blueguy]

I bet dry rot.

Check all the black rubber "T" fittings around the fuel rail, TB, and LIM

 

[Norman LaCoste]

Im having the same problem. The dealer says I need a new PCM. No check engine light. Internal short or something. Sending signal to the throttle. First thing in the morning its ok. I can make the idle stick high almost on demand holding the brake in drive and pushing the peddle. When its doing this it shifts funky like 4500 rpm most of the time. At lights ive been popping into neutral and dropping it befor i go. Hopefully wont cook the tranny befor its fixed.

700 bux though at dealer is crazy, 20 at the wrecker, but all i read is i cant just swap pcm's. But im gonna try first. then maybe order one on the net for 125 with my vin, and they will program.

got an 03 gt 3.8,

 

[Fivefingerdeathpunch]

You can find a 03 PCM and try swapping it for cheap, thats quick atleast. Just unhook the battery, unbolt the PCM and swap it.

I assume you've tried unplugged the TPS sensor as well as the IAC sensor and seeing if the idle drops or stays the same.

And made sure the thorttle cable is not kinked and is not stuck sometimes.