Motor idling slightly rough. Real issue is constant stuttering under load in any gear with flashing SES.... So far plugs and coils changed. Intake manifold gaskets changed as well as smoke tested for vac leaks. Precats were clogged and are now gutted along with warpspeed y-pipe install. Any positive info welcome. Need to solve asap.... I pray its not a blow HG.

 

Well, get yourself and ODBC reader (such as ) and find out what's wrong. If the SES light is flashing, there is something wrong and the ECU is trying to tell you. The only problem is that you are not listening.

 

.... yeah so obviously i have a full obd2 equipment to know this is the ONLY code the ecu is throwing. was my post even read?

 

Since you did a smoke test its probably not a leak in the exhaust manifold or anything like that. The next thing I would check is the spark plug/ignition coil wiring since we know it's not the spark plugs themselves. I don't think we have spark plug wiring in maximas so definitely check the harness.

Also this page (http://www.random-misfire.com/) says hesitation under load could indicate dirty fuel injectors, or a bad fuel pump.

 

P0300 is one of the hardest codes to diagnose. You said you've changed all coils and plugs, were the OEM branded coils used? Were the plugs properly gapped before installation? because SOME do not come pre-gapped. Coils are a PITA and non OEM coils can sometimes be spotty at best.

 

thank you both for the feed back. turned out to be a faulty injector. all replaced now and running better than when i picked the car up in november.