from the sound of it the problem could be four fold.

1.the fuel distributor could be going bad .
2. the fuel regulator could be going bad
3. u have a leak somewhere in the vacuum system
4.check for gas leaks around the fuel distributor

any of these four things could easliy cause the problem

number one is my best guess.....try to find a used on in a junk yard this item is very expensive new.