iddles fine when cold as it warms up it will iddle rough after warm iddles good

It could be many things, unfortunately and without experiencing the problem first hand or being able to do some basic diagnostic tests its hard to say. I would first look at the ignition system, with the engine running get a spray bottle (like Windex) fill it with water and spray the spark plug wires and distributor cap, if the ignition insulation is good the engine idle speed should not change but if the wires are bad the engine will idle rough. Look for vacuum leaks. If the engine has higher mileage when was the last time the valve clearances checked. That engine has "shim" adjusted valves.

My 89 4cyl does the exact thing. I think the O2 sensor is giving the computer bad info. during warmup but mine is welded in. Might want to look at that if you have high mileage.