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Old 07-24-2009, 01:34 PM   #1
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rsg3 is on a distinguished road
Join Date: Jun 2008
Location: Denver, CO
Posts: 35

1999 SL
Default Engine Revving Randomly / High Idle?

Yesterday, while sitting at a light, my RPMs went up from the typical (750rpm) to about 1500rpm without me touching the gas. After checking to make sure the gas pedal wasn't stuck on the carpet, I gently touched the gas to see if that would 'un-stick' it. It revved normally, but went right back to 1500rpm, eventually climibing to 2000rpm or so. When the light changed, I started driving, and everything was fine (normal idle) the rest of the way home, so I thought little of it.

But this morning on the way to work, it did the same thing, except it revved to about 3000rpm. The next time it idled (after about 10 minutes of highway driving), it was normal.

My initial thought was a sticking throttle body plate, but it seems like tapping the gas pedal would 'free' it, at least temporarily, and that doesn't explain why the idle would've gone up yesterday. I cleaned the TB about a year ago and it wasn't very dirty to start with.

It's a '99 SOHC 5speed with 71k miles. I have a ScanGauge and the TPS data look normal and there are no lights or codes. Car runs great otherwise, idle was never high before this. Haven't changed anything lately except thermostat (Stant 195) and coolant. ECTS is brass.

Could it be the IAC valve? A mechanical issue with the throttle cable / body? Something else entirely? Thanks for any suggestions.


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