We have a 2004 Chrysler PT Cruiser with 60,000 miles on it. It is the 2.4 DOHC engine. The car runs great most of the time. But when the A/C is on, and you go to take off from a stop, the engine hesitates sometimes. We put new spark plug wires on and we had a tune-up done last year. Any idea what the problem could be?