My 1998 Dakota with the 3.9L cams at idle the engine speed varies by 100 RPMs at idle. What could be causing this.

 

Clean the IAC, on the back of the Throttle Body. I just did this to a '98 3.9l. Man was it dirty.


If it's not dirty, it will need to be replaced. It won't fix it right away, drive it for a bit, shut it off and go again. It will thin out.



It's held on by two torx bits, T-25s.




Hope this helps.

 

I already cleaned and replaced the IAC and it didnt fixed the problem. Could it be the cam shaft position sensor?

 

It's possible. In the cases I've seen when they've gone bad, the truck wouldn't run.


Could always replace it and see, if it don't work just return it.

 

i don't know a whole lot about the 3.9 but when my 4.7 started doing that it turned out being the TPS, i replaced that and everything was good

 

i hate the idle on these trucks i like my idle to just sit there when its idling like my old cherokee did mine is all over the place but usually around 600...maybe cleaning the tb would help a little but the tps sounds like a reasonable choice too my would idle bad and surge at speed went it went bad