I have a 94 Z28 and had an issue with it idling when it was warmed up after about 20 minutes of driving. It would rev higher 500-1000 rpm's while idling and would cut out at higher rpm's as well 4-5000 range. I replaced the spark plugs and found a bad spark plug wire, but still having the same issue. I had a local shop check the fuel pump and they said fuel pressure looked good and thought it would be a good idea to change filter since it looked old and was in-expensive to replace. The issue was still going on and they told me it was more than likely a bad Opti-Spark. So I spent the 235 bucks on a new unit and had them install it today. The short time I drove it today it seems to Rev quicker with the new opti spark than the old which is great..... but at higher RPM's it feels like its not getting fuel and falling on its face. It also wasn't reving up at low rpm's this time while driving when car was warm. I suggested maybe a bad injector, but the shop said it would be an issue at lower rpm's as well. I also suggested that is could have a vacumm leak some where and they checked that out already and found nothing. No engine codes are displayed. I checked mass airflow sensor and filter and look good. Could it be a bad coil or anything else? I also have a power programer that I used for a non stock tune...gears, tires, different shift points. Should I go back to Stock tune and see if it changes the situation? Getting frustrated tired of spending money on this issue. Thanks in advanced for any help and if you need anymore information let me know.

 

run the car for codes, thats always where you wanna start. these cars get real expensive when you start guessing and throwing money at the problems.

 

If you have something like the Hypertech, it should not cause the issue you speak of. It sounds something like heat soak and things like the fuel pump, icm, coil and others can cause what you describe. Sounds like the shop working on it don't really have any idea what it could be. I replaced my icm and coil to eliminate them and it turned out to be something else. Short of testing these part when they are doing it, I just went ahead and replaced them. They are something you could do with simple tools. The fuel pressure sounds good, but if they tested it on a cold car, then its not really going to prove anything. Doubt it is fuel, since it is not the usual symptoms of a dying pump.

 

Well, I drove the car yesterday for a couple of hours and it never rev'd up during idle which I believe that changing the opti spark eliminated that issue. Today I changed the spark plugs again since the shop said I shouldn't be running bosch platinum plugs since they have caused issues in the past with GM vehicles. Since I changed out the plugs with Ac Delco, I no longer have the issue of losing power at higher rpm's. Crazy how the platinum plugs caused that issue. I'm glad my Z is finally running good and appreciate the comments. Thanks

 

This site is great for info like the plugs. Reading old posts and searching has helped me in so many ways. Its like a manual with live techs ready to help for free