Ok, first thanks for having me. I've been a reader of this place for a while, now. Here's my problem:

1989 dakota 4x4, 3.9 5 speed.

Sometimes it idles rough, sometimes not. Oil pressure went down from what it was usually, which means the gauge now reads straight center.
I'm afraid it may be the oil pump, and hoping it is the idle control.

The truck idles fine sometimes, sometimes not. I adjusted the idle so it wouldn't die when stopped as often. (yeah, band-aid on a bullet wound) Driving or coasting in gear, no problems. When off the throttle, it stalls and quits when I push the clutch.

The idle control on my truck is nothing like that in the diagram in FAQ. It is on the side of the TBI. A small acutator looking thing with a small piston that pushes the linkage on the side of the throttle body. The only thing on the back of the TBI is the fuel regulator. I checked all the vacuum lines and they are good. I replaced the valve cover gaskets as well as the TBI gasket.

Still the problem continues. I have already bought the oil pump and screen, just haven't done them yet because of the engine/front pinion/tranny mount that is tying all those together. (The mount is blocking 2 oil pan bolts.)

Here is the thing: I already have the aforementioned parts, I don't know if I should return them for the idle control. I can't find a pic of my idle control and none of the parts places online have a pic.

Hope I was clear enough with the issue.
Thanks to everyone who could help!

 

Ya most likely it is the IAC. It may the actuator with the linkage. I'm not to familiar with those engines. If you wanted we that the parts manual in the FAQ and the links for online factory service manuals. Hopefully one can tell you exactly where it is. Maybe if you have to go to a parts store. Ask to see it. Then go out to your truck and see what looks like it.

 

Is there any way to get at the oil pan bolts without pulling the engine? Since I have the parts, I'd like to put them on anyway.

The IAC on my truck was unplugged when i got it about 8 months ago and it ran fine.
I did plug it in when I got home, and this idle issue is getting me a bit bothered.

 

Your gauge now reads straight center is fine my 90 has been there since new. Bad would be if at low RPM it goes down. Think you have to lift the engine to get the pan off.

 

The IAC can easily cause your idle problems...
If you take out the IAC and can push the pintle down easily, it needs replaced. It is quite simple to replace because it's so easy to get to.

 

I'm having a similar problem with a 91 dakota 3.9L Came into my shop running very poorly. Idle surge, missing, stalling, when going on a test drive it would run "OK" until just before you want to shift where it would suddenly "loose power/fuel". It would bog, buck and sputter. If I floored it, it would rev up like normal. If I could get it going down the road, it would sputter and buck when throttled back, just cruising. If I give it gas it would accelerate OK but it seemed like it was getting no or low fuel.

Took a look at the fuel filter, it was brand new. Tested the fuel pressure it was 15-16 which I think is right for the 3.9L Put a new fuel pressure regulator on and it only seemed to help a little. It would idle a bit better but still sputtered and bucked. Tried a new TPS and it made no difference. New MAP sensor, tiny bit better. Finally ended up putting a new fuel pump in, a tiny bit better. Now I can actually start out go through 1st, 2nd, 3rd, 4th just fine but only if I'm giving it gas. If I just hold the pedal steady and cruise it starts to sputter and bog down. Giving it a little gas stops this. Checked all vacuume hoses and didn't see any isses.

It seemed like every part & piece I replaced made it a little better but nothing really fixed it completely.

I'm at my wits end and ready to put a pipe bomb in the thing and collect the insurance money!!

Any other ideas you can think of I might be missing? Know where i can get some explosives?

 

It may be possible the fuel Injectors are dirty. Take them off and clean them up.

 

Got a new idle controll and it was worse than the old one! Yup, the motor must be pulled to pull the oil pan.

So, took all the old parts back because the truck seemed to "fix itself" after a couple days' working on it. Only thing now is it idles high after the throttle is touched and hot start problem that for some odd reason is clearing up.

No B.S. I've never had one or even heard of one doing a self fix.

 

When I put a new IAC in my truck it idled high for a few days until the computer figured out what to do with the new part. I probably should have reset the computer after replacing it, and you might want to consider doing just that. If its been more than a week since you replaced it and its still messing up, then you could have gotten a defective part.

 

Oh thank's, Mine dosent even reach the middle of the guage anymore unles it runs at like 2200RPM's and above and at idle its in between the 2 low lines