I just finished swapping a 3.8 in my 97 f150 (after the whole lower intake leak and bent rod thing) It runs really smooth at higher rpms, but shakes like crazy at low rpms or idle. No codes or anthing. Any advice? possible vacuum leak?

 

I had a vacuum line off of the intake on a 3.8 shake a lot at low RPM and not throw a code. It was on a van so I had to feel, not see it, because it was buried.

 

Bump -

okford98, did you solve the problem. If so, what'd you find wrong?

 

Depending on what year 3.8 you put in, they are balanced different than a 4.2. You may have to use the flywheel and balancer off the 3.8. I believe it was the earlier 3.8's that were different. I don't think they changed until '00 or '01. There are quite a few 3.8 to 4.2 conversion questions on www.v6power.net .