Hello, I am a brand new member of this forum. I have a 1992 300ZX normally aspirated, 5 speed manual. I have owned it since 1994. I have been encountering an intermittent problem with it ever since. Here is a fairly typical scenario of when it is most likely to happen: I am driving on a highway. I am approaching an intersection where I want to make a 90 degree turn, so I push in the clutch. I put on the brakes. Then I start turning and the car shuts off. Happens more often when I have the air conditioner on. Happens on both left and right turns. Does not happen every time. In fact, some years it hasn't happened at all. However, yesterday it happened five times in one single 10 mile trip. It was very hot yesterday and I had the AC on and the fan on full blast. And yesterday I wasn't even turning when it happened. I was just coasting up to a stop light. It happened three times in a row on consecutive stop lights. Then I turned the AC off and it kept running at the next three stop lights.

Given that I can not reliably reproduce this problem, I am at a loss as to what I should ask my mechanic to do about this. Is there any other debugging tips or suggestions that anyone has? Thanks in advance.

 

What is the car idling at? On my 93NA, when my idle is set to 600, when coming to stop the car (stop sign, red light, etc), the RPM dips and then goes back to 600. Started doing that decades ago, and increasing it to 800-900 fixed it. The Idle dipping much below 500 can stall the engine. Sometimes. 4 months ago I got a tune up and the idle was set back to 600, and when I got it home it started stalling occasionally again. i knew what was wrong and reset the idle back to 800-900 rpm and that stopped the stalling. It has not happened again in months. Car runs great.

Try increasing the idle speed. Real easy, all you need is a screwdriver and to turn the Idle Adjustment Screw counter clockwise to increase the idle RPM. Count the number of turns so you can back it off to where it started if needed. The Idle Adjustment Screw is on the drivers side near the firewall.

 

Here's a picture of my tach at idle. I had driven for 10 miles, so it was warmed up. I did not have the AC on when I took the pic.

I'm not sure how many RPM's my tach is showing. I noticed that the hash mark between 2 and 3 (for example) (yellow arrow) is right in the middle of the 2 and the 3. So that obviously indicates 2,500 RPM.

But the hash mark between the 0 and the 1 (green arrow) is closer to the 0 than it is to the 1. So does that hash mark indicate 500 RPM, despite not being in the exact middle of the 0 and the 1?

 

I thought of another question:

I found some instructions online for how to adjust the idle speed. It says to warm up the car, then turn off the engine, then disconnect the yellow AAC connector, then start the engine, then adjust the IACV adjustment screw such that your RPMs go to 650, then reconnect the AAC connector, then the RPMs should raise a bit.

But I am wondering if I need to bother with disconnecting the AAC connector? I am tempted to leave the AAC connector connected and simply turn the adjustment screw counter-clockwise. Maybe I'll start a quarter turn. Then check the idle speed on my next drive. If the idle speed doesn't get bumped up to your recommendation of 800-900, then I'll just give it another quarter turn and try again.

What do you think about this plan?

Thanks.

 

I did not remove the AAC, all I did was turn the adjustment screw counter clockwise to raise the idle to 800+. Now when it dips a little when stopping, it dips to 600 and back to 800 and does not stall anymore.

Just keep track how much you turn the screw.

 

Hey @FlyingT, it's been a year now and I haven't had the problem since I adjusted the "Idle Adjustment Screw" per your instructions. I initially gave it a 1/4 turn and that helped but didn't totally resolve the issue. Then I gave it another 1/4 turn and now we're golden! I spent (literally) 30 years dealing with this intermittent problem. Thanks so much for helping me. I appreciate it.