Mechanics

HOW TO ADJUST IDLE SPEED?

1990 Nissan 300ZX

How do you adjust the idle speed on a 1990 300ZX, right now it is idling at 2000 rpms and need to get it lower. Any tips?
Avatar
Dalamb13
April 8, 2012.




No adjustment magically adjusted itself that high. Look for a vacuum leak. First inspect the rubber hoses for signs of cracks or splitting. Next, with the engine still cold, use a spray bottle to spray water over the engine. Look for gaskets or hoses where the water gets sucked in and the engine momentarily slows down.

Caradiodoc
Apr 8, 2012.
Thankyou. Bought the car last week and am trying to get some problems fixed. Found several vacuum hoses that were not plugged in, but had sticks shoved in them. Have no idea why though. But we plugged them in and that is when we noticed that it was idling kinda high. It doesn't seem to have the power that it should; do you think that could be vacuum leaks too?

Tiny
Dalamb13
Apr 8, 2012.
Yup, absolutely. Your car uses a mass air flow sensor in the fresh air intake tube. That tells the Engine Computer how much air, by weight, is going into the engine, then the computer commands the corresponding amount of fuel to go with it. Any air that sneaks in through a vacuum leak or an air leak in that tube after the sensor will not get included in that calculation so you won't be getting enough fuel. There's your low power.

A vacuum leak will raise engine speed but there will not be an increase in power at the same time.

There should be a vacuum hose routing diagram under the hood to show where all the hoses go. The fact that someone plugged them previously suggests there was some other problem they didn't know how to diagnose, or some other component broke or stopped working and they just tried to bypass it. That means there will likely still be a problem once all the hoses are reconnected correctly.
AD

Caradiodoc
Apr 8, 2012.
Okay thankyou very much. Will check that out thankyou!

Tiny
Dalamb13
Apr 8, 2012.

AD