idle not smooth

[Bigjo-NH]

When I stop at a light the idle does not seem smooth, the tac says 600 never fluctuates but it acts like a miss but it don't. I have changed the plugs ,cap,rotor. I have cleaned the TB and replaced the IAC and adjusted to spec. Other than that it runs great at all other throttle positions. It is an 89 with 17000 miles. all stock. Any Ideas?????

 

[VetteGarage]

Check out the injectors. Use a digital voltmeter.. With the engine OFF: Unplug the electrical connection to the injector, measure the resistance you get when you prob the injector. Should be, I think, around 16 ohms. All the injector should be about the same. I recently replace all mine on my 89. I runs great now.