just thought i would ask what the common causes for surging would be seems to do this when ever it feels like doing it pretty commonly i might add it will rev 600rpm to 800rpm and just keep jumping like that till im moving ?? ive replaced plugs,wires,cap,rotar,tps,map what else might cause it ? also cleaned the iac

 

How is your refrigerant level? Sounds like the A/C is low and the compressor is cycling. Try unplugging the compressor and see if it clears up in a few miles...

 

I think the 3.9's just do this naturally, when I was researching out dakota's i read a review that said they idle sporadically. At least mine has since I bought it about 10,000 miles ago.

 

yeah mine does as well (being a 4.7 idk how relevant this is) but sometimes it will drop down to only about 400 rpms then will surge up to about 800 rpm... if you have replaced that much stuff on yours, than i would assume that it is just natural for these engines to do that...

 

try cleaning your throttle body, especially that IAC solenoid. in all 105,585 miles ive drive my dakota, i have never seen her idle sporadically. the 3.9s are known for being a tad bit violent with the vibrations at idle, because of the weird firing order and how the crankshaft was set up. thats what i read about awhile back.

 

yeah i also heard that the TPS might sometimes go on the fritz and cause problems like this

 

mine surges a bit but maybe max 600-650-550 range at most...

 

i guarantee you have a cracked or a loose vacuum line somewhere, thats what causes sporadic idle the most other than the IAC.

 

yea wouldn't dought it!

 

well im not unplugging the ac i dont have ill spray the engine bay and see if idel increases good way to check for vaume leaks right? anyway as far as cleaning it if i dont end up doing the swap then shes getting a v8 tb anyway