heres one thing im trying to think real hard on....
im not sure... BUT...
im pretty sure this didnt start until right after i got my intake manifold gasket replaced about 3 weeks ago, but the thing is im not sure, of course i was paying extra attention right after the repair to make sure they didnt mess anything up but i can remember if this misifirng was prior to that or not
Yeah, I usually replace injectors around 120K to 140K. Generally makes things work better all around, and prevents failure in other areas.
Hey guys I'm new on here but, I had the same problem with my 98 5.7. The intake and head gaskets were the victim of Dexcool. The intake was leaking antifreeze into the cylinders just enough to dampen the plugs and cause a misfire. Once the engine ran for just a little bit the plugs would clean up and start firing again. I yanked the heads and rebuilt from there on up. Just check the plugs after it has sat for a day or so or start it and let it run for about a minute, shut it off before the miss goes away and then check the plugs and you should be able to find exactly which plugs aren't firing just by the condition of the electrode. Good luck
I would pull the spark plugs and check how they look. Also, it would be a good idea to determine if the misfire is occurring on 1 or more cylinders, and determine which cylinders are misfiring. You can use a spark tester tool for this. If all else fails, replace your spark plug wires and spark plugs (if you haven't recently) and see how it runs then.
If all cylinders are firing, but 1 is still misfiring, it may be a faulty injector. In order for the engine to run you must have fire, air, and correct timing.
As for the Timing, as an engine warms up the timing will advance. Check your timing to make sure it is correct. You may just have to align the distributor or change a timing belt.
As with anything, test the most likely culprits before trying to replace anything. Replacing parts that may otherwise be good can really add up quick, and just about every mechanical or electrical part can be tested one way or another.