Windstar 3.8 sputters at 4000rpm's. replaced air intake sensor. replaced clam sheii gaskets and gromets. still missfires at 4000rpm;s. help.

I ASSUME THAT YOU MEAN THE INTAKE PLENIUM GASKET IF THE TUNE UP CONDITION IS NEW OR ONLY A COUPLE OF MONTHS OLD RULE IT OUT BUT I THINK YOUR PLUGS ARE OLD AND OUT OF GAP AND ONCE YOUR SPEED INCREASE'S TO THAT LEVEL RPM'S THE SPARK IS TRYING TO ARC OR JUMP TO FAR TO MAKE CONTACT CHECK THEM AND GET BACK TO ME AND CHECK THE BOOTS THEY MAAY BE CRACKED AND LEAKING + VOLTAGE TO - GROUND IN THE HEAD, ALSO YOUR THROTTLE POSITION SENSOR CAN BE WORN OUT IF YOU STEP DOWN ON THE PEDDLE AND THE RPM'S INCREASE AFTER YOU GET TO THAT SPOT THE SENSORS BAD BUT I STILL THINK YOUR PLUGS ARE WORN GOOD LUCK STEPHEN