i have a 1994 z28 with 190000 miles. sometimes it will run perfect and other times it will idle high/low. the main problem is alot of the time it will start sputtering and back firing while im driving. before it would only do it if i would drive it for long periods but now it gets in moods where it will do it as soon as i start car up...not sure what the problem is due to the fact that it doesnt do it all the time. replaced fuel filter and still acts the same

 

Pull the distributor cap

 

I would check the fuel pressure also and when was the last time it had a tuneup? Any check engine lights?

 

no check engine lights at all.