High Idle

88-GT · Mar 30, 2005

Well just got the car out and safetied yesterday and everything is working great besides a slight idle problem. The car is an 88 GT, still speed density with some bolt ons. The problem is that while driving if I give it moderate amounts of throttle the idle seems to jump up, usually linear with the amount of throttle that I gave it. Almost a fast idle of sorts, and it wont let me kick it down. The only way to get it back down is to turn the car off and start it again, it will even work while still rolling. Anyone have any ideas? I was thinking about the sensor that tells the computer the cars speed but im not sure. Thnx for any help you may provide.

Michael Yount · Mar 30, 2005

First step is always to pull the diagnostic codes and see if they'll help you dianose the problem. Autozone will usually do it for free.

The idle speed is controlled by the computer via the IAB solenoid (3" long X 1" diameter cylinder mounted at about a 45 degree angle on the front of the throttle body). For some reason, the computer is trying to increase idle, not let it idle back down - or components are not working right - the solenoid itself can become quite grunged and need thorough cleaning.

Whatever you do in response to codes remember to disconnect the battery for long enough to kill the computer's memory so it can start over fresh with the changes.

dstanggt50 · Mar 30, 2005

when the idle jumps, you can disconnect the tps and plug it back in, if the idle corrects itself, should be the tps, at least that worked for my old 87

sandman0023 · Mar 30, 2005

I had the same prob. I fixed it by disconnecting the battery for about 20 min. Then I started the car and unplugged the IAC with the car running and then plugged it back in. No probs since. That was back in Sep

88-GT · Mar 30, 2005

Michael Yount said:
First step is always to pull the diagnostic codes and see if they'll help you dianose the problem. Autozone will usually do it for free.

The idle speed is controlled by the computer via the IAB solenoid (3" long X 1" diameter cylinder mounted at about a 45 degree angle on the front of the throttle body). For some reason, the computer is trying to increase idle, not let it idle back down - or components are not working right - the solenoid itself can become quite grunged and need thorough cleaning.

Whatever you do in response to codes remember to disconnect the battery for long enough to kill the computer's memory so it can start over fresh with the changes.

Any good tutorials on how to clean this? I assume you are talking about taking the actual sensor apart...is there alot of part in there or is it fairly simple. Im fairly confident but I dont like messing with little parts that fly out at me when i take **** apart, thanks for the help soo far.

HISSIN50 · Mar 30, 2005

88-GT said:
Any good tutorials on how to clean this? I assume you are talking about taking the actual sensor apart...is there alot of part in there or is it fairly simple. Im fairly confident but I dont like messing with little parts that fly out at me when i take **** apart, thanks for the help soo far.

here is one of the better write ups i have found:

http://www.muscularmustangs.com/iac.html

each page covers a different aspect of the cleaning and idle setting procedure.

good luck.

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