throttle response, press and nothing, then accelerates

the problem of throttle response has gone on for months. Frist reported at 7500 mile oil change, told that is the way it is. Now at 16000+ oil change they attempted to diagnose and nothing. the problem is intermittant. However, if you are an intersection making a turn RT or LF and step on the gas it will hesitate for 2-4 seconds and then go unless you put it over 1/2 the way down. Today when parked I started the car and it reved to over 1000 even when warm, put it in gear and no response from accelerator in spite of being 1./2 floored. Had to shut the car off and restart, still had fast idle but in gear the accelerator responded. This is more than an annoyance as when making turns with oncoming traffic the delay in throttle response is getting dangerous. Dealer at a loss.