I purchased a 1990 BII manual 4x4 with 93k miles a few months ago for my winter vehicle. Up too last week it had no problems and I really have started to like driving it. Then one night after dinner it started to stall. As long as I gave it gas it was fine, but every time it had to idle it would just die. The next morning it ran fine again. Then a few days later the same thing happened on the way to lunch. Then on the way back from lunch it started to idle around 3000rpm! Of course that night it was fine again.

So after a trip to the shop, they told me i needed a new ICM and they also replaced the IAC. They said there was a previous error code that indicated that the tach signal had been lost to the computer. Now the idle is a constant 500rpm, even when cold. It has stalled a few times when still cold because it seems to have trouble keeping it at such a low idle and eventually stalls. Once it gets warm now though everything is good except for the low idle. (It used to idle at about 1000rpm when running good). I would be ok with it now but when its idling the alternator is not producing enough current so all power accessories go dim.

So I guess I'd like to know what the idle speed should be? Seems like it should be at least high enough to keep the alternator producing enough current? Any thoughts would be great...

 

850 RPM

 

I would pull the codes, sounds like the ECU is having trouble controling the idle speed. This will show up in the KOER test. See the tech info post for the procedure.

 

Assuming you have a 2.9, here are some things to try.

Pull the air intake off of the throttle body. If it is black with gunk, get some throttle body cleaner and spray it down with the engine off. I used STP, and was pleased. Wipe it clean. Warm up the engine, make take a while if you are in the midwest this weekend, brutally cold. Pull the IAC plug off and adjust your idle speed to about 650 rpm, then plug the IAC back in. It should come up to 850. If it does not you have a problem in the circuit, or your computer hasn't learned the proper setting of the new IAC yet. You can keep driving it for about 100 miles and it should be all set by then. If not then you have another problem. Your TPS may also be bad, it is just a rehostat connected to your throttle, at the throttle body, that tells the computer you are at idle or WOT. I removed mine and tested it with an ohm meter. Basically it should NOT have any dead spots as you turn the adjuster from one positions to the other with an ohm meter conntected to its leads. Kinda works like a house light dimmer if you know what I mean! I know this is a lot of stuff, but those are about all there are to check. Good luck.

 

Just an FYI, you don't need to adjust the base idle screw, its normal for it to die/almost die when the IAC is unplugged.