Misfire Diagnosis
 

Hey everyone, so I have a 1999 Express 2500 with a 5.0L L30. it has been sitting for 5 years. But starts and runs great. Cant even tell its misfiring until the engine light comes on.

So Cyl 3 is the one that is misfiring. It only misses at idle. It is pretty much a dead miss.

I swapped Cyl 1 spark plug and wire to Cyl 3, the misfire stayed on Cyl 3. Has Spark.
It had injector pulse and the injector was not leaking down, and dropped the same as the rest.
It has good compression, same as other cylinders.

I changed the injector for Cyl 3, thinking maybe that it was staying open and the test just didnt show it. Still misses.

Changed Cap and Rotor just to try. Still misses.

Ran ACDelco upper engine and intake cleaner through it, seems to miss a little bit less then before but still misfires.

Now Im thinking its possibly a sticking valve??? I know the fuel probably isnt helping being that old, but since its only misfiring on Cyl 3, I figure I can rule it out for now. Any suggestions or thoughts???

Thanks for any help.