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-   GM Standard IFS Trucks & SUV's (https://forums.off-road.com/gm-standard-ifs-trucks-suvs/)
-   -   excessively high idle? (https://forums.off-road.com/gm-standard-ifs-trucks-suvs/107661-excessively-high-idle.html)

**DONOTDELETE** 02-15-2002 05:29 PM

excessively high idle?
 
After I adjusted my valves and timing, I got my 89 350 running again, but the idle is really high in Park and Neutral, about 3000rpm. When I put it in gear, it slows to normal. The idle has been like this since I purchased the truck a 6 months ago.
Since this engine is computer controled, the idle is not adjustable. How can I lower my idle?


Thanks in advance,

Tim Moore


**DONOTDELETE** 02-15-2002 06:40 PM

Re: excessively high idle?
 
Sounds like you may have vaccum leak. Check the gaskets and make sure all the vaccum ports and hose fittings on the TB are covered.

90 Z71

**DONOTDELETE** 02-15-2002 11:22 PM

Re: excessively high idle?
 
If I remember correctly, the IAC valve(idle air control) has something to do with the trucks idle, hence the name. If you are standing in front of the engine, it is located on the left side bedind the tbi. It is known to get covered with carbon and all kinds of soot, possibly leading to bad idle, which can be easily cleaned with the proper cleaner. I like to use 3M throttle plate and intake cleaner every once in awhile, works great.You can use it on the IAC valve too.

"Don't you think this outlaw
bit's done got out of hand"---W.Jennings


**DONOTDELETE** 02-16-2002 10:36 AM

Re: excessively high idle?
 
There is a vacuum line behind the drivers side head that has a tendancy to rub either the firewall or the trans bellhousing. this is prevailiant in the 87 to 91 trucks because of a harness clip that has a tendancy to break.
Check it out (have had to fix a lot of trucks for this exact problem) and look at all the vacuum lines and also all of the PCV valves. If it still does it, have the Power brake booster checked (could be a torn diaphram.

Lotsa luck!


**DONOTDELETE** 02-16-2002 04:01 PM

Re: excessively high idle?
 
Take a 17mm or 18mm? wrench and remove the IAC motor. Its a stepper motor that adjusts the Idle using a signal from the ECM. Disonnect the wire harness running to it and see if it makes a difference. You should have a code being set. Do you?

If it don't fit force it, and if all else fails get a bigger hammer!

oletater 02-16-2002 04:20 PM

Re: excessively high idle?
 
"Don't you think this outlaw
bit's done got out of hand"---W.Jennings
--redhalfton, did you get that from a song? if so which one?

http://bbs.off-road.com/wwwthreads_u...sig-edited.JPG

**DONOTDELETE** 02-16-2002 04:40 PM

Re: excessively high idle?
 
Oletater, yeah thats the name of a song off a cd of his called "Waylon Jennings:Greatest Hits", its a great cd for the Waylon fan. If you have realplayer you can go to www.cdnow.com or amazon.com and hear a portion of the song, or any song for that matter.



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