Hi,
I just purchased a 1998 ford expedition. It runs great but at idle its pretty rough. When you sit at a stop light it idles rough and around 3rd gear (40-50 mph) it kind of runs rough. I thought it might be a coil but the check engine light is not on! It has new spark plugs and has had 3 coils replaced(unsure of what coils I purchased from a dealer) so I think it might be a vacuum leak? Please help!!!
Thanks,
Nate

 

Are there any Pending Codes?

 

No there is not

 

There is a problematic vacuum/PCV elbow at the rear center of the intake that like to crack, break, or clog. Check that elbow to see if it's in good shape or not.