I was driving home last night, going through our local town. Truck was fully warmed up, and was holding speed at 43-45mph. The truck was in overdrive (auto trans) and the tac. was at about 1350-1400 RPM. The engine started "surging" and the tac. was moving up & down verry rapidly. About a 200 RPM variable. You could hear the engine changing exhaust notes, going whum, whum, whum, whum, whum. (Or something like that) matching the rise & fall of the tac. needle. It's kinda weard. Now here is the interesting thing, our freind has an '07 Jeep Wrangler "X", with a 3.8L V-6 and 4 speed auto trans. There Jeep has started to do the exact same thing! They have taken the Jeep to the ther dealership 3 times, and the dealer, so far, has been unable to fix the problem. Has anyone else also experianced this problem? If so, was your dealer able to fix it? I'm not realy shure if it is a trans problem or an engine problem, but it is not giving out any error codes. (In eather the Dodge OR the Jeep.)

 

Did you figure out the cause of the problem to this? Tom

 

4 year old thread but first guess would be EGR.