1985 300zx hessitates

Asked by Jan 31, 2017 at 07:41 AM about the 1985 Nissan 300ZX 2 Dr STD

Question type: Maintenance & Repair

Hey guys i have an 1985 300zx na.  Just bought this car.  It
is very hard to start when cold.  Takes a gew tries starting
the car before it stays running.  Once it reaches operating
temp it has a slightly high idle.  If you try to rev it up in
neutral  as long as you dont go past 50 percent throttle it
revs and runs perfect.  But if you go past 50 percent it will
rev to 3500 and fall on its face.  Like you cut the ignition
off.  It will fall to 1000k and shoot back up to 3500.  You
can do this over amd over again.  When driving its alittle
more sensitive.   About 35 percent throttle and it will do the
same until you let off the throttle.  But runs perfect as long
as you stay out of the throttle.  Have changed plugs wires
oil change cleaned mas sensor.  Changed fuel pump.
Checked for vaccum leaks and intake leaks.  Chamged tps
and made sure its adjusted properly.  Used seafoam to
clean carbon from valves.  Cleaned intake and throttle
body.  Nothing has changed.  Can anyone help

4 Answers


WOW, WHAT A CHICK CAR THIS WAS IN 85, good luck with her OK, check the pressure regulator and vacuum lines, and change the fuel filter. You may have fuel leaks where the lines connect to the fuel pressure regulator Injector leaks, this is checked by placing a fuel pressure gauge in the feed line to the rail, watching for static pressure drop, it should be about 40 PSI

1 people found this helpful.

The cold start injection system is a bit finicky on these, it's usually the sensor but have seen the injector fail as well. As CometGuy stated, fuel pressure is a critical on these, also check for proper air flow into the fresh air tubes, not uncommon to find a rodent has made a nest in there. Exhaust back pressure is another problem on these, so you might want to get that checked. Have you tried reading the flash out codes yet?

Ok will check the fuel pressure today. I have visually checked all fuel lines injectors and rail. No visual leaks. Have pulled the vaccum line off the regulator to see if the diaphragm was leaking by. No luck there. And ill change the fuel filter as well today. Thank for the advise.

I currently have the air box out so its getting fresh air. I have not chexk the flash codes yet. What is the procedure in pulling the flash codes?

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