1989 Chevy Celebrity

May I ask, did you do any testing before you replaced the icm? Why did you replace the icm?

Are there any codes? If your losing spark and injector pulse intermittently, the first thing I think about is the crank sensor. Without that signal, there is no spark or injector pulse. The crank sensor is about 20 bucks, the icm is about 100. I'm not telling you to replace anything, but, a problem with the rpm signal, I test the cheap part first.

Did you check for B+ and ground at the icm. You need to test, when the problem occurs. Yes, tracking down intermittent problems can be a pain.

You could try to troubleshoot this yourself? Doing some of the basic tests and checking for codes is easy.

If you had the icm replaced recently, I'd call the shop and talk to them. A lot of shops will replace the coil pack-- plugs and wires-- along with the icm, encase one of the other issues caused the icm to go bad.

Your obd1, you don't need a code reader. You can use a jumper wire between the A&B terminals at the data link connector, then turn on the key, no crank, just turn the key till the dash lites come on. The mil should start flashing, you count the flashes to get the codes.