Hello fellow 1st gen dakota owners. I have a 1995 4x4 with the 3.9lv6 auto trans. I have been trying to trace down its misfiring under load and other weird running symptoms for over a year now. I have tested all components and replaced some and all are at service manual specs. Im almost certain that a bad PCM is the culprit. I just figured out yesterday that when I unplug the IAC while running, the PCM does not put out a CEL as it should like when i unplug other sensors (i.e. TPS etc...). I can drive it all day with it unplugged and it will never pop code 25 like it should. Weird thing is that it seems to run a little smoother with it unplugged. I know the IAC is good, ive replaced it and when plugged in I can see it move in and out for adjustment. but when unplugged, it will not trigger a CEL.

So please could someone unlplug theirs while running to verify that a CEL is supposed to pop up and a code 25 is supposed to be triggered? If so I will be looking for a replacement PCM. much appreciated thanks.

 

The IAC will not cause missing issues. If it is missing that means 1 or more cylinders are not properly working. It might be a bad fuel injector or wires or power supply or bad coil, spark plugs, plug wires cap or rotor. Or engine work is needed in bad piston rings or piston or cracked head or block or a bad engine gasket.

 

I have exhausted all of those other possibilities already. All I want to know is the answer to one question for double verification. Is a check engine light supposed to be triggered with a code 25 if you unplug the AIC while running? according to the service manual it should and I just wanted to verify this with someone as my computer does not do this.

 

Have you done a compression test and a leak down test?

 

Crazy gave you the answer in the very first sentence of his reply. No the iac will not cause the check engine light to come on. Also as crazy asked have you done a compression test yet or a leak down test to make sure the rings and valves are good? Also keep in mind that any electrical components that you have replaced are not 100% guarantee to be good. There has been alot of people that have bought sensors and they be bad right out of the box. Need to have the injector timing and flow checked also. Have you checked the notorious splice under the pdm?

 

no I have not done a compression test yet. I need to do so. but the misfiring is intermittent and some days it will run decent and others it will have almost no power and hard misfire. I am leaning towards the pcm due to the inconsistency of this and other weird things like the tachometer jumping around and occasionally it will lock itself out of overdrive without me even touching the OD button while im going down the interstate.

 

It was a bad pcm. I replaced it with a used one and now the truck runs so smooth and good hasn't run this good since when I first bought it 2.5 years ago