Idle wanders

[Ruby Fan]

I have an '85, stock, except for Borla exhaust. Purchased used, 50K now, a real beauty. The only thing that bugs me is that the idle does not seem to stay at a steady pace. The tach may read 650 for a while, then pick up a bit, then drop down to 550. This goes on and on, sometimes stays smooth. There is no stalling it just drives me nuts that this happens. Could there be a vacuum leak? or weak spring in the dist? I always feel strange to accellerate, but it never stalls or cuts out. Other than that, car runs fine. Thanks

 

[David-F]

It would be helpfull if you could get a hold of a scan tool and have a look at some of the data. Block learn and Integerator, O2 voltage and TPS. I suspect the problem lies in a slow O2 sensor, when the O2 sensor gets old they slow down and don't respond quickly and with the slow ECM on an 85 you can get idle surge as the ECM tries to control fuel mixture but keeps over doing it because of the slow responce of the O2 sensor. Dirty throttle plates can give you a poor idle and even tip in stalls but uasualy no and idle surge. An engine miss can give you and idle surge but that seems to be more common on LT1s not on L98s. But a scan tool would real be a help, I would like to know what the ECM is doing.

David Fulcher

 

[68Roadster]

Had this problem on my 85 as well.....never fixed it before trading it in...
Mechanic had told me to try replacing the intake runner gaskets in case they were old, brittle and causing an intake leak....
Cheap fix if it solves the problem...

Good luck....

 

[steelblue75]

A dirty throttle body will cause erratic idle, clean it up and see if it helps

 

[gmjunkie]

I've corrected this problem on several L 98's,Some times a slow O2 sensor,but more often than not I've found a GOOD Cleaning of the Throttle Body, IAC Valve and passages fixes them right up!!!!