Ford F-150 - 1997-2003 :: 2002 - Throttle Feathering While Cruising

I just had an exhaust manifold replaced on my F-150. It has the small 8 cyl.. While the manifold was leaking, the truck of course ran like crap.....spitting, sputtering, barfing, etc.

Now that the manifold work has been done, the truck runs pretty well, except for some intermittent increase in throttle (not by me) when cruising at highway speeds. This is comparable to the "feathering" of the throttle that you would do when checking for engine noises.

Hard to explain without feeling dopey, but kind of a mild ruuum, ruuum, ruuum out of nowhere when I'm cruising along. I drive a 5 hr. trip every weekend, and it will do this about every 10-20 minutes.