This article is from the Chrysler-Plymouth-Dodge FAQ, by Dr. David Zatz with numerous contributions by others.
This may be caused by leaking vacuum hoses or mechanics
disconnecting your vacuum hoses. If you like to breathe, and you want
your car to perform well, replace all of the vacuum hose it costs
maybe 10 cents per foot. Just get a few yards and do
it one day (warning: you may need different kinds or sizes. You may need to
bits of the old stuff into the shop). Make sure hoses are not kinked.
Vacuum leaks caused by leaking hoses that look okay to the naked eye may
result in the following diagnoses by mechanics:
* Need new carburetor
* Need new transmission
* Need new engine
* Need valve job
* Need new mechanic.