My Mustang has a problem of stalling out when I start it when the engine is warm. I have to rev the motor to keep it running. Once it is started it doesnt stall. Another problem that I have is that when the Mustang is warm or cold, I rev the motor to 1000rpms, once i let off the gas, the rpm drops to around 400 rpms and than revs up to 1500rpms and back to normal idleing range. It also drops the rpms down to around 400 when i step on the brake pedal hard. Would this be a vacuum leak? Or am I going in the wrong direction?