1988 D21 P/U with Z24 Engine: Idle surges Up and Down

[marc780]

My 1988 D21 pickup with Z24 engine and 290,000 miles - runs strong when it is moving, but at idle, especially when warm, the idle is uneven.

The engine is on its second valve job and has had new rings (10,000 miles ago), always passes smog, run strong, but i have had this problem for the last 10 years - uneven idling. Compression is strong like new, spark plugs are new, timing chain and gears are new, catalytic convertor is near new; alternator puts out a steady 14 volts - anybody know what it might be thats causing the surging idle? I have checked for vacuum leaks and the timing was reset to pass smog...anybody have any ideas?

[Big-Bird]

There are several electrical components attached to your TBI. Here's a quick look at them



Check for loose connections first. But it could be the Throttle Sensor & Idle Switch. NM50 might know. He's a nissan tech.

[NM50]

The idle does this to try to find its target speed.The first thing to try is vacuum leaks.With the air cleaner housing on spray carb cleaner around the intake.Usually the throttle body gasket is sucked in.If that doesn't change the idle then post back.