Hi everyone, I just recently swapped out my 3.9 TB with the one for a 5.9L. The power is very noticeable BUT it appears my gas mileage is suffering. And not just that....My rpm sits at about 1300 (used to be like 900) at park and neutral and when i shift into drive it drops to 1000. After driving it for a while and putting it into park it will then sit up at 1500!! its driving me nuts! anybody kno what to do? one more thing im still using my v6 tb cable (cut off metal piece it goes under so it would work). Could my tb cable be the problem? i mean it drives fine besides the rpm crap.

thanks
-jake

 

it sounds like it might be sucking air. I would say either tighten it down some or take it off again and get another TB gasket. If the gasket is like rippled or not perfectly right it will suck air and idle at higher RPM's. I would also look to see if your throttle cable is the right length. Basically just make sure it's not so short that it is holding open the butterflys slightly even when not pressing the gas pedal.