i just changed the head on my 99 mazda 626 4 cylinder.... everything went smooth i got the timing right too, and now when i start the car it will start and the engine runs fine too if i am giving it gas if.... when i hit the gas pedal, the rmp kinda goes up and then comes down and if i hold it at 500 rmp it will stay there for alittle and come down and then go up again, if i let it go it just dies on me. no check engine light comes on... any idea would be great thanks