1985 Nissan 300ZX Runs rough while cold

L337BG

MEMBER
1985 NISSAN 300ZX
6 CYL
2WD
MANUAL
84,000 MILES

When given a cold start, especially in high humidity, the car has a hard time starting up (turns over just fine, but can take 3 or 4 seconds to actually start). At this time, if I attempt to drive, it runs really boggy, it almost feels as though I'm tapping on the accelerator and jerking along, even though I'm maintaining a consistent pressure on the pedal.
As soon as the thermostat moves the tiniest amount, the car becomes completely normal and runs smooth as can be.
I have no idea what the problem may be.
I've checked and sealed all exhaust leaks, checked for vacuum leaks, made sure all electrical was sealed.
I have no idea what the problem would be and it's incredibly frustrating.
Any ideas would be helpful.

2 Replies

RASMATAZ

MECHANIC
75,992 POSTS

Inspect and test the cold start injector and the coolant temperature sensor

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Saturday, July 24th, 2010 AT 4:49 AM

STEVEDONATO

MEMBER
1 POST

The answer is;
1985 Nissan 300ZX Runs rough while cold

Cronic lean surge condition that some 84-85 cars suffer from. While warming up in open loop operation the computer thinks the engine is warmer than it actually is due to either a bad chts or harness or bad signal interpertation and leans the mixture to much causing the lean surge. After about 2 minutes of warmup the fuel system goes closed loop when the O2 sensor comes on line and the engine then runs fine.
You can try replacing the chts and harness but that probably will not fix the problem.
If your car is an NA the best fix is to swap in a 1987 computer. ($50.00 new) That will fix the problem and give you a better running engine across the power bands.