I have a 96 Suburban which is idling roughly, but smooths out with acceleration. I have been getting a check engine light with a trouble code of P0305, misfire in cylinder 5. I have replaced the plugs, wires, cap, and rotor with no improvement. I just had the fuel injector spider replaced with the MPFI upgrade, still no improvement. EGR valve has been checked and is OK. Intake manifold has been checked for vacuum leaks and is OK. Air intake has been checked and cleaned. I have read that these engines require/like AC Delco parts only. I will be replacing plugs and wires to AC Delco tomorrow. My mechanic's reader shows misfire at idle, but the misfire disappears with throttle. Any ideas? Thanks!

 

Welcome to the forum. A misfire just means the suspect cylinder did not contribute sufficiently to the crankshaft output. It could be spark, air/fuel, or compression. Maybe you have a low compression issue with #5.

 

EinST, thanks for your reply. I notice you are from Virginia. My son goes to Patrick Henry College in Purcellville. VA is a great state. Anyway, I have replaced everything I could think of and then took the car to my mechanic for the Injector spider replacement. I haven't replaced the coil before, however, I would think that if the coil was going bad, then more than just one cylinder would have a problem. I can't seem to figure out what could cause issues in just one cylinder that I haven't already replaced or checked. What is interesting is that the rough idle smooths out with acceleration and the code P0305 goes away during acceleration. It seems to be only a problem at idle. Would the Idle Air Control valve create a problem in just one cylinder?

 

Do you remember how the spark plug looked out of that cylinder? Consider asking your mechanic to check for compression issues. You may have leaky valves or rings, just enough to affect the idle (more time to leak).

 

i agree. my personal experience turned out to be leaking valve stem seals. the cat converter was soaking up most of the oil smoke, so i saw none out of tailpipe. but a huge miss at idle, and sometimes at freeway speed. run compression and leak down test. this will tell you alot.

 

Thanks, I'll give it a try.