# Up and Down Idle



## RobertBlevins (Nov 6, 2013)

Hmm. My 1988 HB with the 2.4 NAP-Z does this:

Starts up as soon as you turn the key, runs fine. 

Quick and peppy, good power, no dying-at-the-stop-sign issues as long as you warm it up for about thirty seconds. 

Idle surges up and down constantly. Goes from around 600 up to 1400 RPM. Up and down. Up and down. 

Once in a while, the Check Engine light comes on. Eventually goes off after some miles. Been doing this about six months now.


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## SPEEDO (Jun 9, 2003)

sounds like its hunting, start with checking for vacuum leaks, may even check for any codes


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## StansB13 (Feb 11, 2003)

Vacuum leak like has been mentioned.
See if you hear any hissing while the truck is running. Or you might get lucky and find the leak with your hands (I had a v-leak once that was behind the air inlet to the air cleaner), get it to stop hunting and locate the leak that way.


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## rogoman (Dec 16, 2004)

The proper way to check for a vacuum leak is to attach a vacuum gauge to a full vacuum source. With the engine fully warmed up, the reading at idle should be 18 - 20 InHg. At 3,000 RPM, it should be around 21 InHg.

If readings are under 18 InHg, check the intake manifold nuts to make sure they are tight. The gasket may have failed; spray a water mist at the gasket to see if the gauge reading changes. Also check the intake plenum bellows at the throttle valve and at the MAF for cracks or loose clamps.


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