Blew the head gasket on a 1994 5sfe last week. Sent head out to be machined and reinstalled with new timing belt, and engine seals. Engine fired right up 2 days ago and settled immediately into a nice smooth idle. After 10 minutes or so, it started skipping and rpm's fluctuating. Using the gas pedal, the engine was roughest at idle and just above idle, say up to 1500 rpm or so. Above that it smoothed out. Tried it again yesterday and same thing. Before firing it up, I did a compression check and all was normal. Spark plugs looked normal. Engine started up smoothly, idled smoothly and was smooth thru entire rpm band. I put the car in gear and drove about 1 mile down the street and turned around. By the time I got it back home, the same problem reappeared. So for now the problem only exists when its warm. I replaced the ECT sensor but no help. Any ideas??

 

Other then the head gasket problem, was the idle OK?

Did you reinstall all the components, wiring, etc correctly?

The throttle valve has a couple of coolant hoses going to it, make sure the coolant is circulating.

Idle is controlled by the IAC valve.

Sometimes the coil can crack and cause problems.

Are the spark plugs the correct ones?

Check the fuel system items such as fuel pressure regulator which responds to intake manifold.