So i have an 87 iroc z with a 305. Everything was fine up until a couple of months ago. The car now has what seems to be a very random misfire at idle only. I have changed the distributor cap, and rotor, plugs, and made sure the plug wires were connected well. I even tried to diagnose this random misfire by removing plug wires, it had no effect at all. I think it might be the coil, or an injector, but im not quite sure. Also i checked the resistance on each injector, and it was the same for all of them at 16.9 ohms i believe. As well as listened to the injectors to make sure they were opening.

 

Could be anything in the ignition. ICM, coil, burnt plug wires, whatever.