I have a '90 vert that has been having problems lately and i cant figure out why. When i bought it last November, it ran perfect. It did a ~30 second AWS warmup, idled steady at 750, and the only issue on the test drive was a loud pop from the exahust which i didnt think much of. Fast forward to March 2020 and it runs okay, but the idle is rough. Sometimes it misfires while I'm driving but mostly it misfiires at idle and during the AWS system. Sometimes it idles steady at 900 and sometimes it bounces up and down between 1000 and 100 to the point where my car shakes at a stoplight because it gets in such low rev range. Sometimes it will be idling pretty steady (somewhere between 800-900) and then all of a sudden it misfires like crazy and nearly dies. The symptoms are hardly consistent. I have replaced plugs and wires to no avail. I think it may be low on power but i cant really tell because i havent owned it for long and only startred daily driving it this march. Ive only been through 3 tanks of gas on it. Any ideas on what could have gone horribly wrong between the near perfect test drive and now? any ideas what the source of the backfire, or lumpy inconsistent idle is? car has just over 69,000 miles

 

Hard to say what's wrong without actually seeing the car. Here's what I would suggest doing to begin the trouble shooting process. Start with the simple stuff first and then work your way up.

Have you tried pulling trouble codes? There's a green one pin connector next to the battery. Ground that one pin connector and to the key to the "ON" position. If you have trouble codes, the check engine light will blink the codes. Here's a link to pulling trouble codes: 89-91 CPU Trouble Codes

Have you checked the battery and cleaned the terminal recently? If the electronics in the car isn't getting a full 12V, than that may be causing problems.

Has the fuel filter ever been changed?

Just my opinion, but I like to dump a bottle of fuel injector cleaner into my gas tank with every second fill-up.

 

how do I ground the connector? Sorry to ask, I am pretty inexperienced with circuits.

 

The green single pin connector is right next to the battery. Just ground it by connecting it to the negative post on battery.

 

will do, thanks. I’ve decided that it seems like it’s having trouble staying anywhere below 900 rpms. If it gets under there when idling it tries to save itself it seems and then falls back down, nearly dies at about 200 or so and then tries to save itself again, it’s a bit of a repeating process. Not sure if that helps