Yesterday on the way to work my 2000 Chevrolet Silverado 1500 4WD with the 4.8L V8 Vortec engine started flashing a check engine light. I read it and it was a P0300 Random/Multiple Misfire.
I had experienced a slightly rough idle previously (nothing serious) and had been unable to track it down. I replaced the PCV valve as a course of standard maintenance and it seemed to help get the idle back down, but still slightly rough.
I also replaced the spark plugs and plug wires, and replaced the alternator on warranty for an unrelated issue.
After I got the check engine light, I started doing some more diagnosis with a bluetooth-OBDII reader which is when I found that I had misfires only on cylinders 2, 5, 6, and 8. Since it was on separate banks, I could find no commonality of items to replace, so I tried the following things.
- replaced coil pack in cylinder 2 because it had the highest misfire count, no effect
- replaced the EGR valve, also with no effect.
- did the carb test to look for vacuum leaks in a few places on the intake manifold with no results
- unplugged to MAF to see if the idle improved and it did not (although I didn't try a load test with the unplugged MAF.)
So I guess I'm stuck and about ready to give up on this one and take it to my mechanic, but I was wondering if there was something else I should try or if anyone has any thoughts.
Side note: I only see the misfires at high RPMs (>1500), so could I drive it home if I take it very slowly and rarely open the throttle?