When my truck is cold it runs perfectly. As soon as it gets to operating tempurature it develops a pretty bad miss. It idles rough and bucks terribly at low rpms. I dont think my egr is hung up because it still does it when i remove the vac hose. the egr valve is about 2 years old. Cap, rotor, plugs, and wires are also in the 2 year range. No codes. What else could make it run cruddy when its warm?

 

Ignition Control Module (ICM), PIP (stator), coil

All three are common causes of your described symptom.

You can have the ICM tested, the PIP is a little trickier. Coil can be swapped.

 

Relevant to the 4.9L I-6:

It would probably be worth your time to change out the TB gasket. Mine was sucked all the way into the contours of the idle air passages. Here's a video that walked me through it. It's a very inexpensive fix, but you'll make a mess cleaning out your old throttle body:

 

I cleaned the throttle body and replaced the gasket with no change in behavior. icm and stator? is the stator inside the dizzy? wheres the icm? coil was replaced with my last tune up but I could swap another one in being that they are so cheap.

 

Gas Filter is next. I think there's a very good chance this will make it right.

 

Yes, the stator (PIP) is inside the distributor
For reference: Stator

The Ignition Control Module (ICM) is located on the distributor ('91 and earlier) or mounted on a heat sink near the driver side hood hinge ('92 and later).

 

ohh I actually did the icm once on this truck. its on the fender on my 92 like you said. looks like im gonna be fooling with the dizzy if the fuel filter doesn't help. ill look in the book how to test the icm.

 

I don't know of any reasons why ignition system performance would fade when the engine gets hot. You can always check for spark with a spark tester, which is basically a dummy spark plug that you ground with a clip and a see-through window that makes it easy to watch for spark. If your truck starts and runs at all then the test is redundant. Do you have any CEL codes? That Hall Effect sensor inside the distributor is a real pain to change, and won't always be fixed by buying a new distributor from the parts house. In my experience, they cause a no-start or sudden failure condition rather than fade with heat. If the gas filter doesn't make it right, it's worth your time to do a solid diagnostic with a good multimeter (Fluke) and an oscilloscope. Hopefully it doesn't come to that- just did mine about 6 months ago!

 

don't mean to but in but as mentioned you need to pull the codes again and do you have a catalytic converter on your truck what do you have as far as tools like a volt meter vacuum gauge or a back pressure gauge things of the nature.