High rev idle - 300ZX Nissan Cars & Trucks

As long as the idle air control valve is working, ( I assume this is what you replaced, I would first check to make sure it is operating correctly), If it is, then Id begin searching for a vacuum leak

Define idles high like its going high rpms before shifting or the engine itself is high reving if its high rpming when shifting its mostly you tranny going out you can try tranny fix oil I used it on my truck when it had shifting problems and ive had no problems since it takes a few days to work though and if its the motor itself it could be a lot of things but I dont know much of the problem based on what you told us

A high idle meant there is excess air bypassing the idle control valve. Check for vacuum leaks. Also the throttle body may be sticking open or the throttle cable not adjusted correctly.

When a car is idling it is at rest.The idle setting refers to the engine revolutions or 'revs'.If the setting is increased so that the 'revs' are greater,the engine will not stall at rest.This is 'high idle'!

idle air control valve
Best regards
Ck

high revs are usually caused by a vacuum leak, pinch each line one at a time,

Most likely need the idle readjusted. Your vehicle has a high idle rev limiter that will shut down the motor to keep it from getting damaged. Make sure your accelerator line isn't being pulled on. This will pull on the gas pedal just like having a foot on it and will rev the motor as well.

try replacing your idle control censer it is normal for a car to idle high for a short period when it is cold but only for about 60 seconds

it will idle high with air con on and revs will go up and down try turning air con off it that fixes it then there is no problem

Throttle position sensor.