C4 Tech/Performance L98 Corvette and LT1 Corvette Technical Info, Internal Engine, External Engine

inconsistent idle

Old Aug 7, 2006 | 08:58 AM
  #1  
icecream's Avatar
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Default inconsistent idle

I have a 88 vert with 47000 miles. bone stock. all of a sudden the idle started fluctuating. going up and down and up and down from like 700 rpms to 900 then down then up. its very annoying and something is obviosly wrong. i know these motors were prone to getting a manifold vacuum leak. could that be my problem?? i also know there is some time of idle controller moduale. could that be the bad part? i appreciate any insite on this issue. thanks...
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Old Aug 13, 2006 | 06:36 PM
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Originally Posted by icecream
I have a 88 vert with 47000 miles. bone stock. all of a sudden the idle started fluctuating. going up and down and up and down from like 700 rpms to 900 then down then up. its very annoying and something is obviosly wrong. i know these motors were prone to getting a manifold vacuum leak. could that be my problem?? i also know there is some time of idle controller moduale. could that be the bad part? i appreciate any insite on this issue. thanks...
Sounds like the IAC. Look in the tech tips for how to clean the IAC pathway.
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Old Aug 13, 2006 | 06:39 PM
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First . . . Try the idle reset proceedure per service manual...never heard of this?....buy a service manual.
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Old Aug 13, 2006 | 07:37 PM
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WAAAY too many undiagnosed and untested parts replacement recommended in post #2. Don't start out indiscriminately throwing money at the problem. As suggested down the line, get a hold of a FSM and follow the trouble shooting charts indicated by your symptoms. The fact that the idle fluctuates, so, is a pretty good indication that the IAC is working. The ECM tells the IAC (among other things) what to do based on the input of sensors all around the engine. A bad connection or bare wire can wreak havoc. A vacuum leak is the most likely suspect. However maintenance, such as a fuel filter, checking the air filter and cleaning the IAC passages in the TB are never a bad idea.

RACE ON!!!
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Old Aug 13, 2006 | 09:22 PM
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Originally Posted by corvette1989bham
First . . . Try the idle reset proceedure per service manual...never heard of this?....buy a service manual.
Theres a vg step by step in the Forum pages for IAC re-set.

Last edited by davemack; Aug 13, 2006 at 09:56 PM.
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Old Aug 14, 2006 | 12:52 PM
  #6  
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That kinda customer service SUCKS! You may want to get some carb cleaner and spray it along the the area where the gasket is messed up, if the RPMs increase you've found your vac. leak, if that's what it is. That's where In would start. And it never hurts to clean the IAC passages and pintle.

I also think it's , if they took the job, and new something was wrong before it left they should have rescheduled you to come in or proceeded to diagnos the problem.Good reputations are hard to build...but easy to lose.
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