Steve,

Thanks for that description of how vacuum works with the engine and transmission. I'm wondering on my car, there are instances where the car is responsive to throttle input and other times when it is extremely sluggish (throttle position changed a few inches = slow buildup of speed). What are the possible causes in the variation of responsiveness? (Probably hundreds of things). I have tried to determine whether it is ambient or engine temp related but it's inconclusive in my nonprofessional judgement. Perhaps a little more responsive when cold. Are there any things that should be focused on? Just a tired transmission or engine? Bad vacuum modulator? Leaks? I guess the confusing part is the somewhat varying behavior, i.e., leak would be all the time, modulator bad all the time, engine tired all the time. Thanks for any input.