Hi everyone,

recently my Monte has been seeing random spikes in the rpm. There's really no set pattern that I've seen. It'll happen on occasion while I'm parked but also while I'm accelerating or maintaining a speed. The list of stuff I've had fixed recently amounts to the water pump, vacuum tube, lower/upper intake manifolds, one of my coil plugs and transmission cooler lines. When the water pump was getting fixed by a mechanic, coolant got on my coils and shorted one of them out and caused the car to misfire very very badly and that was why one of the coils plugs got replaced. I don't know if the misfiring could've had anything to do with what I'm experiencing now but thats what I'm looking at, at the moment. Any advice is appreciated, mostly looking for a place to start.

 

Does it jump only when driving or even in park?

Do you have some kind of scan tool? Easiest way to diagnose driveability issues is to log the data while its happening. That way you can go back and review the data again and again around the point of issue looking at different sensor info each time.

 

It has done it while in park, but not recently. I don't have a scan tool but it does seem more characteristic of a misfire to me but there's no check engine light.

 

clean your iac valve/sensor, mine did that a while back I removed iac and cleaned with carb cleaner and used q-tips and rag to clean in housing and it fixed it !

 

I had a similar problem with my 98. Check your ignition coils, I had a bad one that would randomly work here and there and made the rpm jump then drop. It's a pretty easy fix to change them out, just a couple bolts on each one then stap into place. I paid about $35 per coil.