High Idle...WTF?

[JEFNLSA]

Ok, I'm driving home from work today and as I get into a little stop n' go I realize that my idle is stuck at 1500 rpms - hence the WTF? I tap the pedal...no change...continue cruising...no change. Stopped by a shop (mechanic there who's done some work for me before) once I hit my side of town, pop the hood and we both look at it. Nothing out of the ordinary, everything looks AOK. No SES, temp looks good, throttle cable stopping where it should etc...

WTF? I'm baffled as was he. So I drove it home and in the garage it sits...any ideas?

 

[6 Shooter]

Maybe you could try rebooting your controller/pcm by disconnecting your battery over night.

 

[Ripp 73]

I have a question. If you let off the clutch slowly without giving the car any gas with the pedal, where does the idel go when rolling? Have you also let the car cool down and started it back up to see where the idel starts and then drops to when warmed up? I do like 6 Shooter's idea about disconnecting the battery over night.

 

[C4Tom]

Developed a vacuum leak? Intake?

 

[Evolution1980]

I'd hook a diagnostic computer up to it (OBD-II, I think) and see what your sensors are reading. I suppose that if a few sensors aren't reading correctly, it would effect idle. however, then you'd likely have a code, so....hmmm... yeah, maybe a vacuum leak like Tom suggested. Vacuum can be a ***** to hunt down. Possibly you have a softend hose that is collapsing?

 

[gmjunkie]

I'd check the IAC valve and EGR valve!! If either is sticking or has a piece of trash in them can cause this, and may or may not trip a code!! And a vacuum leak is a Possibility!!

 

[6 Shooter]

I do remember that little plastic vacuum valve under the passenger fuel rail cover giving up the ghost on my LT4.

 

[Evolution1980]

I'd check the IAC valve and EGR valve!! If either is sticking or has a piece of trash in them can cause this, and may or may not trip a code!! And a vacuum leak is a Possibility!!

Don't IAC's typically stick shut, causing the car to sputter at idle? I guess if it can stick closed, it can stick open...

 

[gmjunkie]

Don't IAC's typically stick shut, causing the car to sputter at idle? I guess if it can stick closed, it can stick open...

No!! It can just be sticky and cause a erratic Idle,no idle or fast idle!! The EGR can act the same way!! And it don't take a Big piece of trash either!!(smaller than a pin head!!)

 

[Evolution1980]

No!! It can just be sticky ... And it don't take a Big piece of trash either!!(smaller than a pin head!!)

Yup, that's for sure. On my old daily driver, over time a small accumulation of airborne particles had collected on the pintle and gotten gunked up causing it to stick.

 

[JEFNLSA]

Update:

I start her up this morning and she's fine. It's gotta be the TB hangin' up which is what Bill -aka the ZFDoc- thought it was. After work I'm going by the his place to do a little surgery and clean her up at the same time. Should correct the problem.

Thx for the help everyone...I'll post results of fix.

Jeff

Btw..If it turns out that I am wrong, at least I have some other things to check out thx to you guys. From what I hear though, the BBK TB's are notorious for this...