I have a 95 Dakota with 124k on a 3.9L. Truck runs great when engine is cold, as it warms up the idle speed drops to 300-400rpm. When you put it in gear and give it gas it will stall and die also smells like it's running rich when it warms up. Any thoughts would help. Thanks !

 

Probably a bad O2/oxygen sensor and maybe a bad IAC Idle air control valve.

 

I have already replaced the IAC, will try the O2 sensor. Took it to Oreilly's and pulled the codes (sense key cycling only gave me a code 12) The trouble codes I'm getting are below-

47-battery voltage problem
21- o2 sensor volts too high
42- auto shut down circuit relay
43-Spark ignition control circuit problem

As of now I plan on replacing O2 sensor and Ignition coil. What are your thoughts on the auto shut down relay/ battery voltage?

 

UPDATE: I replaced the 02 sensor and crankshaft sensor (crankshaft sensor was all gummed up with oil). It has a small rear main seal leak. Now the truck runs worse seems to miss. Not sure where to go next!

 

Make sure the battery is charged all the way otherwise replace the battery as Dodge vehicles have no sense of humor with low voltage. low voltage will alot of times make the vehicle run like crap. It has happened to me already and than I did alot of research on it.

 

Thanks moparnut, I had the battery tested CCA were below rating so I replaced the battery. No change, truck still runs very poorly and starting to backfire. I had the ECM codes erased. It threw a code 21-02 sensor related. I had just put in a new Bosch 02 sensor (ordered off ebay) before it started running like crap. Do you think the new sensor is bad or could there be a bigger problem due to an ignition issue or possibly exhaust plugged up (appears to still throw plenty of air out of the tail pipe ?

 

Backfiring and missing was due to the crankshaft position sensor. The "new" one I bought didn't work right. Put the old one back in and seems to run much better. Still stalling out at parking lot speeds.

 

I have an '88 4x4 with a 3.9 v6 139k that is doing the same kind of things. It will run at idle in park ok, though a little rough. In gear it wants to stall out every-time I come to a stop. I've replaced the IAC already. was told it could be an bad O2 sensor or bad MAP sensor. IDK, was going to start swapping out sensors, but was looking for a little advice from other owners first. bought the truck recently for 1200 because the previous owner was tired of chasing the gremlins and he didn't need it anymore.

 

Throttle Position Sensor was the first thing I was told to change when I had revving issues.