I have an 89 IROC with 5.0 TPI - have done a complete tune-up. Runs great when cold - starts running a little rough when hot - if I re-start the car (when hot), it runs good for about 30 seconds and then starts running rough again....any suggestions?

When it is idling rough, it seems to smooth out in gear, but is still a bit rough.
thanks for any help!

 

Maybe thermostat isn't opening fully.

 

When you say hot, do you mean normal operating temperature? How high does your temp gauge get?

 

When the engine is cold it operates in open loop, which means it uses preset tables in the computer, and ignores most sensors. When the engine is at working temperature, it operates in closed loop and it responds to all sensors. It would seem that you have one or more sensors that are not working properly. In these old cars the ECM only looks for the presence of the sensors, and not able to tell if the sensor output is proper. You can use a scan tool to look at the sensor outputs and see if they make sense for the conditions.

 

also, can you describe the roughness? is there any fluid loss? how do the plugs look, and does it smoke? is there any possibilty the engine has been worked over?