Hi Tech guys. I have a 1999 Pontiac Grand Prix, 3.8L V6, no turbo, 155,000 miles. When the car is in park at idle, approximatgely 1000rpm, it will surge up to 1500rpm, then down to almost a stall, then back up to 1500rpm, back dow to almost a stall, and so on. it will do this intermittently. it runs fine at street or highway speeds, but when i brake to a stop, or in park, it can start doing this rpm surge up and down, and sometimes stall. it will start up right away after a stall.

Recent engine work includes injectors and fuel rail cleaned off-engine by service station (two weeks ago), new fuel filter when injectors and rail installed; new plugs, wires and coil pack approximately 10,000 miles ago.

Thanks for your help