High idle (about 1500-2000rpm) 1980 280zx

Clamp air regulator tube it might be stuck open.

If you can get the engine to lower its idle by pulling up on the gas pedal. You may want to check out the dash pot on the throttle body. Its the white round thing that looks like there should be a hose hooked to it. On the underside of it there is a spring loaded rod that pushes on the throttle. Some times that will get stuck and hold the throttle open slightly. It is adjustable and may be out of adjustment.

You may also have a weak throttle return spring.

If when you try the pull up on the gas pedal method and there is no change. Then check for vacuum leaks. When you are sure that there are zero vacuum leaks try adjusting the idle screw. If you adjust the idle screw and get into trouble like you can't remember how many turns in or out you made. Or the engine won't idle at all after you adjust the idle screw. Just turn the idle adjustment screw clockwise till it stops. Then turn the idle adjustment screw six full turns counter clockwise. That will get you close enough to try again.

One possibility for a vacuum leak that you may have overlooked is the auxillary air regulator. The air regulator is part of the cold start system. The air regulator has a bi metal valve inside. When cold the valve is open to allow more air to bypass the normal idle bypass in the Airflow meter. As the engine temp rises the valve closes slowly eventualy stopping the air flow through the AAR. Causing the Rpm's drop to normal levels. As someone else said before you can test to see if air is passing the AAR by pinching off its hose with a pair of needle nose pliers. If when you pinch the hose the idle drops then air is leaking passed the AAR. That will cause your high idle. The hose we speak of comes from the boot between the Airflow Meter and the throttle body.

You should refer to your FSM for more info on the AAR they have diagrams and everything. Good luck and let us know what happens.

What happened when you turned the idle screw down? The point of my suggestion was that if the engine died when the idle was adjusted to the proper rpm than the PO adjusted it up to keep it running, why? What condition caused this. Is there a vacuum leak that makes it have to be adjusted that high? The first thing is to find out if it is adjusted up and why or if like Jeff says if the idle comes down when you pull up on the pedal. Finding out why a condition exists is the first step to fixing it. I wasn't trying to throw useless info at you. The approach you need to take to a new to you car that the PO may have screwed up is to find out why and then fix it right. Many PO's "rig" things up to get by or unload a car. If you want it to be dependable you want it fixed right. Often fiquring out a PO's method of "repair" and/or mindset will help solve other issues faster and easier for you. When I got my 80 ZX the PO had done some strange repair work that I had to undo to fix right. I'm passing my personal experience onto you in hopes that you won't have to find out some of the surprises the PO left for you the hard way like I did. Good Luck with it. I hope you get it running great and can enjoy many many happy miles with your ZX.