I have an 89 Dodge Dakota with a 3.9L engine. About two weeks ago it started running rough in cold weather. Today was about 60 degrees and it is running rough, I would say this is about the cutoff point in relation to the temperature. It runs rough from idle all the way through 60mph, if I keep on the gas it seems OK until I let off the throttle. It acts up on me in the morning going to work but when I get off in the afternoon and the temperature is much warmer it runs fine all the way home. I think it is a sensor problem, but not totally sure. I don't want to start replacing many parts trying to find the problem. I have checked the computer codes and there is nothing there. Any ideas?

Thanks

 

Well first a tune up is best, all ignition parts, fluids, filters ect. Next do you have a Check Engine light? If so get the codes and see what they say. I will move this to the 1st Generation Dakota section.

 

Pull the ACS and see if its oiled up.

 

<n00b>

ACS?

</n00b>

 

Still have no computer codes. I did a tuneup in spring of this year. Checked with a shop that I take my truck to and they told me they have a truck in the shop exhibiting the same symptoms as mine. They talked to a Dodge guru and he told them to change the ignition pickup in the distributor, supposed to be a known problem. I replaced the part, no help. They also told me that the truck they are working on also has no codes even with an external scanner attached. I have also replaced the coolant temp sensor. I checked the voltage from the tps and it looked good. When I did the tuneup with new plugs and wires, I used a spark plug lubricant. When I took the wires off I noticed that there is a crustiness on the plugs. I used a throttle body cleaner to clean the plugs and wires. Not sure if this would cause this problem. This truck runs great in warm weather. After cleaning the throttle body with the cleaner it idled good for about two minutes and then started running rough and would die. I am looking in my manual and do not see anything labeled as an ACS. Any help is appreciated.

 

Yesterday was in the low 60's and the truck ran like crap. Today the weather was in the middle to upper 70's, the truck ran great. I bought a can of component cooler from radio shack to see if I lowered the temperature of the sensors if I could duplicate the problem. I sprayed the EGR & transducer, TPS, MAP, Idle speed control actuator, fuel pressure regulator, while the truck was running, also checked the spray pattern from the fuel injectors and they looked good. Did not spray the os2, smec, and the plug wires, ran out of coolant. I will start the truck tomorrow morning at 4:45AM and I'm sure the problem will be back. I am going to pull the plugs tomorrow and check the way they look. I have to use the wife's car and I am hearing some flak over this. I would appreciate any help.

 

you sprayed the PCM with contact cooler?

 

If your talking about the computer module, no I did not. They call the computer module on this truck the smec. I think this is a sensor problem but I am not ruling out the computer being sensitive to cool temperatures. The temperatures we are talking about I think, this is unlikely. We are talking difference between 60 something to 70. If it was 30 degrees or 110 degrees, maybe. If you have any good ideas I am all ears.

 

do you have the ability to test the response of your sensors to changes in input signals?

can you do a vacuum test when cold and running rough, and again when warm and running smoothly?

 

Coolant temperature sensor.