RPMs have been slightly surging recently. But on a 100 mile trip, air going full blast, cruising about 75, the surge became so severe, my head snapped back and hit the headrest (no I didn't fall asleep). I babied it the rest of the way home and it only got worse. Has been running ok since. What causes that?

Engine surges while driving sometimes as much as up 6000 Rpms. While cruise is on or off. While it's idled it does it and if you hit the gas it goes down. No solution while driving. Our mechanic said it had something to do w/ when the air kicks on but it does it when the air is off.

Engine surges while driving at highway speeds. Either with or without the cruise set. Dealer can not find cause. Said they were sorry. It will surge from 2000 to 8000 rpm. Bought it new, problem started around 88,000 miles on clock. Have almost 89,000 now.