'90 High Idle

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Dec 8, 2007 | 05:38 PM

jghmczo6

Thread Starter

Racer

Joined: Dec 2004

Posts: 470

Likes: 0

From: Phoenix Arizona

'90 High Idle

My '90 vert is ideling at 900 RPM and jumps to 1200 RPM, have not detected a vacuum leak. It jumps to 1200 when the A/C clutch is engaged once dis-engaged the idle drops to 900. Could this be the IAC or a worn-out TB? Are there test I can run to determine the source? I have noticed the idle does not jump as frequently when in Park or Neutral moreso when in Drive. I do have a FSM, but not sure where to look.

Your help is appreciated............................: cool:

Last edited by jghmczo6; Dec 8, 2007 at 05:41 PM.

Dec 8, 2007 | 06:57 PM

Yellow2015

Pro

Joined: Sep 2006

Posts: 702

Likes: 2

From: Conyers Ga

Check the throttle body for carbon buildup. Could be holding the butterfly open just a tad too much. The idle SHOULD increase when the AC is engaged. Check the TPS for correct voltage, clean IAC valve and last but not least, DO NOT ADJUST THE IDLE SET SCREW. Search here for the TPS adjustment procedure..

Dec 8, 2007 | 09:32 PM

Dads90

Burning Brakes

Joined: Oct 2004

Posts: 898

Likes: 1

From: Pearland Texas

The TPS is unadjustable. The IAC is probably bad or needs cleaning. Vaders' site or tech tips has the reset procedure. That will also set the idle. I've did it on mine and it worked good. If you replace the IAC I would recommend the AC/Delco, the one I got from Autozone was a Wells and I could never get it right. Also I got a good timing light that shows the RPM, the dash tach isn't very good for exact RPMs'. Good luck

Dec 9, 2007 | 11:25 PM

RandyJ75

Safety Car

Joined: Jan 2006

Posts: 3,566

Likes: 4

From: Mt Laurel NJ

St. Jude Donor '06-'07

Quote:

Originally Posted by Dads90

Check you Coolant Temp Sensor. Take the car to a place that can scan the system. A bad CTS will not set a code, you need to scan the system. I had the same problem w/ my car that you have, when I scanned it, the CTS showed a temp of -35 degrees on a 70 degree day. Make sure not to wrap the CTS w/ anything like teflon tape, it will lose it's ground that way. Remember the CTS on a computer controlled car acts like the choke on a carb.

Good Luck

Dec 10, 2007 | 06:14 AM

KeyWestJack

Pro

Joined: May 2006

Posts: 583

Likes: 0

From: Pittsburgh PA

I know you said you checked for a vaccum leak but if your idle goes back and forth between the the higher and lower idle speed it sure sounds like a leak to me.

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