RUNNING BAD!!!! NEED HELP PLZ

[David weaver]

WELL OUT OF THE BLUE FROM TIME TO TIME, WHEN I START UP THE CAR IT GOES INTO A HIGH IDEL LIKE CLOSE TO 3GRAND AND THEN DOENT REALY IDEL BACK DOWN.THEN WHEN YOU DROP IT IN GEAR IT IDELS AT LIKE 2000 WITH OUT EVEN PUTING YOUR FOOT ON THE GAS.BUT WHATS REALLY WEIRD IS WHEN YOU DO GO TO GIVE IT GAS,DEPENDING ON HOW MUCH GAS YOU GIVE LIKE IF YOU GO TO JUMP DOWN ON IT WILL DROP RPMS AND ALMOST DIE.BUT UNDER NORMAL DRINING AND YOU GIVE IT GAS THE RPMS DROP 500 AND THEN THE CAR PICKS UP.I HAVE NO IDEA  WHAT COULD BE THE PROBLEM SO IF ANY ONE HAS ANY SUGGESTIONS I WOULD APPICATE,THANKS DAVID