When I decelerate or coast down a hill several times now my engine hesitates. Quite noticably I might add. I had to change out one of my a/f sensors not long ago so that isn't the problem unless the other one needs to be changed as well. I run nothing less that 89 octane and either shell or chevron gas goes in the tank. My plugs have about 20k on them could that be an issue? Would a bad plug make is miss sometimes but not always. It never happens at WOT. Any suggestions? I have a scan guage and aren't throwing any codes. thanks folks