1990 300zx NA misfire

[brian300zx]

Alright so, still new to the z community. I've had my 300zx for about 3 months now. When I first got it it had codes for a bad coolant temp sensor, replaced that. And I also had codes for the driver o2 but that went away after I reset the codes for the coolant temp sensor. The car is still misfiring and has massive hesitation under 3k but runs normal after 3k. It has new plugs, recently cleaned the maf and throttle bodies. The car also gets really bad gas milage and I can sometimes smell gas (no there are no leaks) if anyone can help me out with this it would be great!

[z.Leinbach]

Would reccomend ohm testing the fuel injectors they should be between 10-14 ohms with about .5 varience. Also look at the ptu on the front of the passanger cams bank check for green crud. In the connectors (our cars are famous for it), i replaced mine and helped cure the problem, also replace the throttle position sensor, sometimes our ladies get alil forgetful with actually throwing a code. Have to set ignition to 15degreese btdc, then the tps has to be set to .45 and then the idle screw can be adjusted, these 100% have to be done in order listed

[DCaff300ZX]

^^^^All good info, do check and be sure to check the injector connectors, PTU harness, CTS and all IACV connectors for the green crud.
However with the fuel smell I'm betting one or more of your old style injectors are done so be ready for the infamous VG30DE/DETT refresh...the fsm in the everything you need to know sticky is your best friend.
Have fun!

[brian300zx]

So this morning as I was about to check the injectors I pulled one of the coil pack connectors and there was no change in idle. Could this be the injector?

[DCaff300ZX]

Yes, you basically performed the power balance test where you remove coil packs from one cylinder at a time until no difference- this isolates the problem cylinder. Now, you need to determine whether you have spark or not at the plug, and if not why from the possible reasons, which are outlined and with tests and procedures in the fsm in the "everything you need to know..." sticky at the top of the page.