Ok, so this is definitely not a new problem with the Maxima... rough idle, misfire on cylinder #4.


A short back-story... just recently replaced the ECM and IAC on this vehicle. I have not done the relearn as yet. I started the car, and it runs poorly. I hooked up my code reader and found the code for misfire on cylinder 4. I got a new coil, started it up, and still ran rough. I checked the code reader, and it still shows cylinder #4. Crap.


So I swapped coils between 2 and 4, started the car and still no change. I checked the code reader, same code message. I read somewhere that it could be the crankshaft sensor, so I looked up the specs on that and tested it, and it tested good. For trouble-shooting purposes, I bought a spark plug for this one cylinder and replaced it. It must have been an original plug because the gap was very wide. I replaced it with a new one, but still runs rough...though nominally better. I will replace all plugs very soon.


The car ran fine, as far as the idle goes, before changing out the ECM and IAC, so that's what's bugging me a bit here. ( I changed the 2 thinking they were the problem, and in fact they were faulty, but the car ran fine.) So, where do I go next for a solution?


Here's what I plan to do next, but please advise if there is something else I should do...


Check oil for coolant, coolant for oil to see if there is a blown head gasket.
Replace all spark plugs
Clean MAF and MAP sensors
Swap coil with a different cylinder
Replace injector
Compression test on this bank of cylinders
Spray carb cleaner around intake to check for leak.


Any thing else that could of help? I'm so tired of working on this car...it's been a very good car until now and this one problem I cannot seem to eliminate. Your help is greatly appreciated.


Thanks,
Darrin