5.7 high idle problem

[BIG_KID]

my 91 5.7 has a high idle problem. No vacuum leaks. I can do the IAC relearn and it will idle perfect all day but when I turn the engine off for 10 seconds then restart its back up to 1500 and won't come down. Any suggestions...

 

[skylark]

I had the same problem on a 90 K2500. It was a bad IAC.

 

[michael hurd]

Sounds like the stepper motor is worn out. Time for a replacement.

 

[Johny Sticks]

As others have stated the IAC is your first place to start. Other then that, perhaps you're timing was set incorectly? I just bought a 89 and the timing was off due to the previous owner not being aware of the ESC, and how it affects timing. Computer could be acting up, though I doubt it. Only other thing I can think of is o2 sensor. And thats iffy

 

[BIG_KID]

I'm going to borrow a timing light and scan tool and check all my parimators. I'm also going to convert to a heated O2 sensor. I thought about the ECM loosing its memory

 

[Huck Finn]

I second the timing, changed distributor in my 89 a couple weeks ago and fine tuned the timing. Noticed a few degrees off it had a really high idle. Just make sure to unplug the connector for the timing adjustment

 

[BIG_KID]

Finally stored a code and check engine light came on. TPS volts hi. Check with volt meter. 4.2 at idle and stays there. Replaced TPS and IAC for the hell of it. Problem solved. Thanks for the help...