get it scanned & check for codes 032 EGR failure and 021 or 022 which is throttle position sensor high or low. I had something very similar happen a few months ago. I think the EGR valve went, which in turn caused the TPS to go. it only took 2 days before it was undrivable. Whenever the car was turned off, it would reset, seem to be fine on a restart then as soon as i stepped on teh gas, the code would throw and the car would suge and buck and not shift gears, very strange indeed. HOpefully its something simple and not as expensive as what i had tho.