Car just started this last month. At hard or fairly hard acceleration it feels just fine, as well as when you try and "hypermile" during acceleration. But if you accelerate under normal power, the tach will jump and the car will surge until you get to running speed, when it will level off. The ONLY time it does it is under moderate acceleration. I have changed the fuel filter, have put over a quart of injector cleaner in the tank since then, and pulled a plug (it looked fine). The car has 78K miles on it, and I bought it 6000 miles ago. It ran perfectly until I stopped for gas one day on the way home (that may have been coincidence). The weird thing is it does not do it every single time, just about 75% of the time.

Any ideas????