if it fluctuates while idling, it could be the idle control motor (I think that's what its called). that's what my car was doing but I just adjusted the throttle cable to make it have a high idle kind of thing
Do a boost Leak test ASAP. It sounds like a leak after the throttle body like PIMking said.
Is the car revving to like 3000 then cutting down to like 1000 then going back to 3000 over and over? If It is then Its a LEAK somewhere. Like a Intake Mani gasket, Throttle body gasket, Injector seals. If you find NO leaks anywhere when doing the boost leak test then look at the ISC and check with a Multimeter.
Also take off the throttle cable and MOVE the throttle by hand... CLOSE it TIGHT immediately after opening it. If it seems to work okay by hand...then It could just be a sticky throttle body. Sometimes people use O-rings for shaft seals in the Throttle body. This can sometimes cause it to move SLOWLY and have a delayed response to snap shut.
Its a boost leak around the TB, Injectors and or Intake gasket. Trust me I thought my ISC was going bad but it was going up and down way too much not like normal Idle surge and stalling all the time and the intake gasket was toast.
Intake gasket is only like $9 and takes about an hour to do.
I am a betting man and I would put money on one of those three.
remember these are old cars the gaskets are not new and holding up very well.
did a boost leak test, not that. it boost awesome. it stalls wen i let off the clutch when first starting up. wont run in neutral wen in low rpm. and there is also a screeching noise when i accelerate from a stop. i have no idea whats wrong