Idle Has a Mind of its Own

[ringleader]

Has anybody had the problem of their 90 Vette idling at 1000 rpm and then the next time your drive the car it's normal and then it goes back up again. I've installed a new throttle body, IAC, oxygen sensor, adjustable fuel pressure regulatior. Mechanic thinks it might be the EMC. Any Ideas?

 

[Hrtbeat1]

According to the Service Manual the 90's tach is an "air gap device" and it gets its information directly from the distributor terminal block. I would check for a bad ground within the distributor being that yours is an intermittent problem. My 90 has something crazy going on with the tach it reads almost 1000 RPM's high at idle and more off at speed. I have been told that the instrument cluster needs repair/rebuilding but I'm still not sure. All the other functions of the cluster are working fine. I have an aftermarket ignition module that I need to swap out with my original to see if that has something to do with it.

Hope this helps.