The Car: 1989 Nissan 240sx - Aristo 2JZ-GTE - AEM EMS V2 - Single turbo kit setup - FIC 750cc injectors and Rail - Aeromotive FPR - Deatschwerks DW300 fuel pump - Russell fuel filter.

Part Replaced : New battery (February 2014), New NGK 3330 plugs gapped at .028 (May 2014) , Newer low miles coilpacks (August 2013) New coil pack connectors & Terminals (August 2013) AEM 3.5bar Map and IAT sensor (January 2012) Fuel system (Spring 2012)

Parts Tested: Unplugged front cam position sensor #1 car ran dramatically worse. so that seems to be ok, will test resistance on it still. Tried known good working ignitior and noise filter, Swapped out to another set of NGK 3330's @.028 Gap. Tested the AEM Map sensor it testeed within range. The IAT sensor tested slightly off so i got a new IAT sensor that tests closer to spec but still not 100% spot on where AEM states it should be, car ran slightly better. Tried known good working Wideband 02 sensor no change, Replaced injector o-rings and bungs after finding out there was a leak when i sprayed choke and carb cleaner around them the car ran different. Once fixed i tried the same test and there was no change in the way the car ran when i sprayed choke and carb cleaner car seemed to run slightly better but only for a little while. Car holds 43-44psi of fuel pressure at idle and climbs when the car comes into boost Fuel pressure doesn't change when the misfire occurs. Tested the new battery that see's 12.8-13.0 Volts when the car is running misfire or not.

Thing's i haven't checked: Having he injectors cleaned and flow tested, but they are only a couple years old and have maybe 2500 miles on them. Crank position sensor, ECU itself, Wiring harness, and the fuel pump (Though the fuel pump if going bad i would see a loss of fuel pressure i believe?

The issue: The misfire/lean issue started last fall (September-October 2013) It was relatively cold out and i noticed it was missing and running lean so i took the car home and thought the 40 degrees. weather is the issue as the car doesn't typically see temps that cold and it was tuned in mid-high 90 degree temps. Took the car out this spring with No changes other than a new battery and it does the same thing, car seems to run better when the engine is cool, But once water temps start getting into the 155+ degree range the misfire happens slightly at idle (AFR goes between 15.8 - 17+ AFR) does the same thing on light and partial throttle. But the car seems fine when you go WOT or give it a certain amount of gas, but almost on tip in it goes lean and trying to maintain speed then it goes real lean and misfires. Sometimes when the car is idling and the AFR's go real high (16-17 Range) the car will die. But it will start back up no problem.

Could bad gas be the issue? We put gas in it just before last fall, then drained it out for world of wheels then put new gas in the car in April, been troubleshooting ever since.