If you mean it doesn't idle at the right speed, then almost certainly it's the AAC valve(auxiliary air control). Can only buy it at dealer. $100
1991 Nissan Hardbody King Cab 4WD Pickup L4-2.4L 2389cc F/I VIN KA24E >
> My truck has not idled right in two years. It runs ok on the highway
> but hot or cold at a stand still it will not idle right and the
> exhaust is gassy smelling. I live on an island in the middle of the
> pacific and the only mechanic on the island can't figure it out. >
> I've replaced all injectors and the computer. Nothing helped. I just
> checked the Mass Airflow sensor. Part # AFH55M-10
>
> A-B = 1.6 MEGAOHMS
> A-C = 1.6 MEGAOHMS
> B-C = 4000 OHMS
>
> Can anyone suggest anything? Steps to take. People to ask, web pages
> to lookup? HELP!