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300Zx-NA running rich - plz help

Hi All: I have an 89 300 non turbo NA car that is giving me a headache. Starts fine, but when put into gear, trys to stall out. On the road the car runs very rough, rich, can smell gas.

Last year I had a problem with similiar symptoms; after R&R on the fuel system, H2O temp sensor switch, plugs&lines, regulator, air filter, etc, turned out to be the MAF (mass airflow sensor). Replacing that fixed the problem and the car ran fine. Until now.

My mechanic, who "knows cars" but doesnt specialize in Z's tells me that maybe the car's just getting old, that newer technologies makes repair and diagnosis easier; but that the problem could be as simple as a 'brain' fix, or a stupid short somewhere in the harness, or some other 2cent remedy that would send the proper signal. The shame is that my car sounds great and otherwise runs fine, it's in top mechanical condition and looks pretty clean for 16 years.

Can anyone help me w/a clue? TIA

riondluz_at==gmail---dot========com

Reply to
Rion D'Luz
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I would do a compression check to eliminate any possiblity of your timing belt having slipped a tooth. Compression would be low. How long since the belt was replaced (miles and time)? Any chance your mass airflow sensor has gone bad again? What about your o-2 sensor? How many miles on the car?

Reply to
duckbill

Did you replace the AIV valve at the same time? If not you have probably killed another MAS.

Reply to
Steve T

Hi and thanks for the reply: Oh Boy, What's the AIV valve? I bought the MAF from Roger @the zbarn after eliminating every other thing we could think of. Is the AIV valve inside the MAF?

Rion

Steve T snipped-for-privacy@yahoo.com wrote:

Reply to
Rion D'Luz

The AIV valve (Air inlet valve which is conected to the exhaust manifold and has metal reed valves in it) starts leaking and dumps hot exhaust gases into the air stream in front of the MAS, quickly killing them. This is a well known problem on those cars. This is the metal box with the vac diaphram on it located right next to the ign coil. Remove the 2 screws that hold the vac diaphram onto it and if the blue rubber plunger is all black, it's bad and is killing the MAS's.

Reply to
Steve T

Reply to
Rion D'Luz

You DON'T want a used valve, get a new one from the dealer.

Reply to
Steve T

Thanx, but my mechanic says its not the valve bec. he disabled it. And now that I replaced the plugs and cables, the car runs better, i.e. not trying to stall out; but still very rough, specially at low RPM's, or when i feather the pedal while accellerating. the machine just seems to hang. but I dont smell gas as much, maybe just a whiff.

If its not the MAF then I'm at a loss as to what it could be. I'd really feel bad letting this car go cuz it's pretty sound in all other respects and I'd like to believe that it just need a tweak to something. But it's also 16 years old and bound to fail on something else, so i suspect that I'd be throwing good money after bad to continue it's upkeep.

Appreciate your input, Steve Rion

Reply to
Rion D'Luz

Reply to
Bitsbucket

don't know if this applies to the 300zx but I had a very similar problem with a 280z and the problem turned out to be a cold start switch....

when the engine is cold this triggers a fuel injector to aid in starting cold...when mine failed it ran constantly...filled the intake with gas! Lucky I didn't blow myself up!

Reply to
beard6801

It doesn't, the 300ZX doesn't have a cold start injector.

Reply to
Steve T

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