Z31 studdering at low rpm

[AZ89two4Tsx]

Okay, here's the dealio. My cousin's 86 Z31 runs great and all, but when it's cold and at low rpm's, it studders a bit. This is when you're on the gas, in any gear. It doesn't cut out or anything, but just kind of "hesitates" if you will. This is on low throttle and if you give it enough gas, the problem does not happen. Any ideas? This is like a mystery problem. It idles fine.

Oh btw, it's a 5 speed and has about 75,000 original miles on it. Digital dash if that makes a difference. Almost every possible thing you can think of has been changed, including almost every vacuum line. Since I'm in town with him, along with changing the oil, we cleaned the maf. He's thinking an oxygen sensor now. But it doesn't seem to be throwing any codes.

Anyone have any ideas? I'm stumped, he's stumped and everyone else he's talked to is as well.

[DoctorRobert]

I have the same thing with my '85 300zx. I just ignore it till it warms up. I'm used to old cold natured cars...

[Infinitiguy19]

This seems more engine related than transmission related. so check the compression, spark plugs....

[AZ89two4Tsx]

Car is mechanically perfect (in theory).

Plugs, cap, rotor, etc.... were already changed.

[Perrenial Badass]

Sounds like lean surge. Can you get your hands on an 87+ ECU to swap in for a cold start test?

Oh... and NA or turbo? What's it idle at?

[AZ89two4Tsx]

No, I can't get ahold of an ecu. I'm in Missouri right now, and I live in AZ.

N/A motor. Idk how I forgot to mention that, lol.

And the idle was adjusted by a mechanic, I remember him telling me that. So it should be oem spec? I haven't driven it so idk. What SHOULD it be? When he got it adjusted, it was at 500rpm, so they turned it up.

[evildky]

I'd have a look at the aicv and the mas

[Perrenial Badass]

Mine sat at 850rpm without accessories on. It went up to... about 1000rpm, maybe 1100rpm with the idle up, can't remember exactly since I haven't drove the f***er in forever and a day.

If everything else checks out, I could lend you an 87NA ECU to test if it's lean surge.

[AZ-ZBum]

Exhaust or intake leak. Check vacuum lines. Check manifold bolts.

[AZ89two4Tsx]

Hmmmmm....I'll be sure to let him know and check these things out. Hopefully it's an easy fix.

Thanks guys.