99 Dakota just replaced the PCM and O2 sensor... Now when at a idle for truck starts sputtering like it wants to shut off, sometimes it even idles up to 3000 rpms at a stand still. also acts like it wants to backfire while running so bad. Any suggestions... Already replaced exhaust and catlic converter.

 

Could it Possiblly be the Mass Air Flow Sensor?

 

Thanks for responding... My husband is a mechanic for Good Year and I asked him that question before, he says mine don't have a mass air flow sensor.

 

Whelp, sorry -- I'm used to tinkering around with my mustang .... Anywho, after a few mintues of research, I would suggest chcking the "Idle Air Control Motor"(IAC). You also said you changed an 02 sensor? Just 1? Might have a Upstream and a Downstream 02 sensor? ... I'm assuming you have the 318 in your truck

 

We changed the up stream O2 sensor, thats what the scanner showed was bad when we hooked it up as well as the pcm. Changed out both parts and reset the codes, lastest a few hours and the check engine lite was back on with the same 2 codes. I tried driving it yesterday but it acted like it was gonna backfire and almost shut off on me so I parked it.

 

well, these things aren't terribly hard to diagnose if you are willing to put in the time to eliminate possibilities. the engine operates based on 3 controlled factors, fuel, air, and ignition. any of those could be the problem. so the thing to do is not just start replacing parts, but determining what is actually working properly. to be any more specific you would have to be more specific in regards to your engine, etc. so here are the basics...


ignition (spark): a good starting point to understand what is going on inside an engine is the read the spark plugs. this involves removing them and looking at the coloring and condition of the part that is exposed to the inside of the combustion chamber. This will give you an idea if you're running rich or lean and it will verify that the plugs are in good condition. if they aren't, then go ahead an replace them. also, one way to check for spark is to remove one spark plug, plug the wire back into it, and turn the engine over a few times while watching for arcing.

air: like that above poster suggested, clean your idle air valve... that is a routine maintenance operation on these vehicles. next start the engine listen for a sucking sound in the engine bay, vacuum leaks are a good source of drivability problems. also, you can use carb cleaner to test for vacuum leaks (caution, carb cleaner is flammable.. don't be an idiot when doing this) by spraying the edges of the intake manifold while the engine is running.. if there is a change in pitch or smoothness of the engine when spraying a spot with carb cleaner then there is a leak there.

fuel: check for proper pressure on the fuel rail. if you have low pressure then dropping the tank and replacing the fuel pump/filter might be required.

if all that stuff checks out ok then you have the basis for further diagnosis, but skipping the basics and replacing parts at random are not a good idea.