Hey everyone, new to the forum, but having been on others for my RX7, I understand the idea of searching for posts and I’ve searched for several weeks on and off for this issue. So we have a 04 G35, manual trans, has a random misfire. The misfire only occurs at idle and at lower rpms in all gears. Once it gets over 2500rpm or so it clears out. It also has sluggish acceleration up until this point, which I’m guessing is connected. We have put factory plugs in it, we replaced the valve cover gaskets also, so the intake gasket is new. I have smoke tested the car, found no vacuum leaks. We also performed the throttle body reset and the MAF reset as well, no change. Really hoping that someone has seen this problem and can help out. Thanks.

 

So it's actually throwing the P0300 diagnostic trouble code yes?

 

Yes it is throwing the P0300. No other codes related to a misfire. I haven't put it on a scantool, so I don't know exactly which cylinders are skipping, but it does go away when it gets above 2500 rpm

 

Firstly, perform the "idle air recalibration" since you had the upper intake plenum apart.

Then I would buy a new ignition condenser, Nissan part number 28351-89902 It's around $10

Also buy one new coil pack and start swapping that one (mark it with a sharpie or something) with all the cylinders. Hitachi part number ICG00007 they're around $35 and Hitachi was the OEM manufacturer for that part.

 

Ok cool. I'll give it all a shot and see what comes along. Thanks. I'll try to keep this posted.

 

Ohh and double check that you didn't accidentally pinch the oil fill neck between the upper/lower plenum. It's VERY easy to do.

Same with the 3 PCV lines, intake tube to left valve cover, the bridge across the two VC's at the front of the engine, and the PCV valve in the right side VC up to the upper plenum. Also check the PCV valve, if it's stuck and sucking crankcase all the time it's going to throw the air volume off particularly at low rpm when there's a lot of intake vacuum.

Also check the brake booster hose on the right side of the plenum, it goes into the battery box, then turns into a hard line, then turns rubber again at the booster. There is also a check valve stuffed up inside the rubber part right before the booster but that shouldn't be the issue unless the hose cracked right there.

Also check your dipstick o-rings to make sure they're there. Yes you can actually have a vacuum leak from the dipstick tube but I've never seen that EVER throw a P0300. I suspect it's a failing coil pack or the condenser.

Sometimes leaks on the brake line stuff are easy to miss from a smoke test because those fittings are all hidden behind the cowl in the battery box/booster area.

 

Yeah I pinched the oil fill neck thing in there. Heard the whistling and smoke tested before and after. No vacuum leaks there. I'll check the pcv too. I'll double check all the others too. I appreciate the directions to go check. It's getting annoying driving like this, I do mostly highway driving right now, so it's not a huge problem.

 

@Joepickett7 I'm curious if you got your random misfire resolved. I'm having a similar issue and this looks like the fix, but would like to hear how it worked for you. My other thought was maybe I got some bad fuel or moisture in the tank.

Thanks,
Michael