Stalls at lights, hard starting, IACV cleaned to no effect

[brokencar]

Hi everyone.

The car in question is a 1985 non-turbo 300ZX with 120,000km. Auto.

Bought it and it ran fine for maybe 20-30km worth of short trips to get it registered and once that was done it started being a right pig to start of a morning - cranking for ages and the idle would fluctuate madly once it did start. After a day or two of that it started stalling as you pulled up at stop lights.

Pulled the IACV and cleaned it with throttle body cleaner - was plenty of carbonisation - unscrewed the little grub screw over the spring, cleaned all that and put it back in. Checked for vacuum leaks by spraying starting fluid around the lines, no change in RPM when the car was running.

The car went well after that evening for a test drive - no stalling. Turning on accessories (e.g. aircon, lights) sometimes resulted in the idle RPM increasing, other times it did not. Idle sat at 1,000rpm or so. Next morning back to the madly fluctuating idle (200-700rpm) and stalling at stop lights.

Above idle it pulls well and is responsive but it bogs slightly when initially accelerating out of the fluctuating idle.

Am I right in thinking that the IACV is stuffed? Anything else I'm missing here?

[evildky]

Welcome to NICO!
So adjusting the screw out isn't helping?
Have you checked the ecu for codes? Sometimes a bad O2 or CHTS can cause a rich condition that will actually bog or even stall the car and it doesn't always throw the code, in these cases a problem like this would be pre persistent when warm.

[brokencar]

Turning the screw in or out didn't appear to make an appreciable difference. I didn't read the FSM well enough to see that it has error codes - I'll check those next. Thanks.

[evildky]

Yup, Z31's use an OBD system, here is how to check it for codes
http://xenonzcar.com/z31/ECUcodes.html

[brokencar]

Showed error 31 (A/C doesn't work... perhaps related) and 23 - TPS or idle. The TPS is for a manual car as was pointed out in my other thread so I'm wondering if having the 3-pronged connector disconnected is causing that error.

The car won't rev past 3k in Drive where it will quite happily in 1/2 or N so I'm wondering if that's related to the missing bit of the TPS. I've found one locally to swap in and see whether that helps, and either way I'll test the TPS with a multimeter.

[evildky]

I believe the second connector for the TPS only affects the downshift and should not throw a code. The TPS code would be for the other side of it, so your TPS needs the connector checked and cleaned and possibly adjusted, if that doesn't clear it up it would need replaced but sounds like you plan to replace with the correct one anyhow. TPS on these cars is simply an on off switch that affects acceleration enrichments. TPS can cause accel issues, RPM related isued usually are a result of the MAS. Could still be ignition timing, or fuel as well.