i have a 94 e420 when i hit the brakes my rpm hand goes below 5 an it act as if it want to cut off but once car comes to a complete stop it would go back up . i put a new belt on it about six months ago . i notice to that the belt tensioner jumping a bit is this normal or do i need to get a tensioner. an where can i get a combination relay from that is cheap. could someome help