'87 Z31 N/A Low Idle UNLESS Parking Lights are ON or warmed up for 1-2 minutes

[Icetera]

I picked up an '87 300zx N/A 2+2 in excellant shape, except for a couple electrical and audio nuisances (mostly fixed) and an idling problem. The car has had limited use for the past 3 years, since the original owner had a stroke and can no longer drive a manual transmission. His wife did drive the car around the neighbothood once a month and had the oil changed each of those 3 years.

When the car is first started, after sitting for a day or so, the engine idles at 500 RPM or under, typically cutting off unless I give it some gas for 1-2 minutes. Afterward, the car idles at the typical 650-750 RPM. The car is due for a tune up, so I figured this is probably not a big issue. While testing the Digital Gauges (I had to pull and clean up the Power Supply Unit to correct an intermittant display issue), I noticed that if I turn on the parking lights, the engine idles fine at around 750 RPM, but with the lights off, the engine returns to 500 RPM. Turn the parking lights back on and the engine idles back to 750 RPM. I imagine there must be a short somewhere between the lights and something within the engine management system, but I have no clue what it may be. Perhaps a temperature sensor? Any ideas would be appreciated, thank you.

[XJared]

Most likely either the base idle is set too low or the idle motor is full of carbon from being driven so lightly over the years.

[XJared]

BTW, If you want, I know an excellent Z tech that lives in Richmond.

[Icetera]

As far as the idle issue in relation to the parking lights, I was unable to replicate it last night, though I could consistantly increase the RPMs with them the previous night. Last night was even cold and snowing, so I think that narrows out a temperature issue in relation to the lights. Perhaps the load from the parking lights was enough pull the engine out of the standard idle state?

Most likely either the base idle is set too low or the idle motor is full of carbon from being driven so lightly over the years.

Consisdering that the engine idles appropriately once warmed up for a bit, would not that eliminate the possibility of the idle being set too low? I will try and check the Idle Motor this weekend and see if I need to clean it out. Hopefully, it is fairly accessable (I did not bring my service manual to the office, today).

BTW, If you want, I know an excellent Z tech that lives in Richmond.

Knowing of a local Z tech would probably be very helpful, as I would like to keep this Z in top shape. Thank you for your response.

[Perrenial Badass]

For cold idle issues on this car, I generally put my money on the CHTS. It's a common problem for these cars, the replacement + subharness is 40-something dollars. So it's a good idea to change it out when doing a timing belt job... as the sensor sits behind the timing belt cover.