1995 Nissan Altima Car dies after shaking

Our car has started, over the last 2 months, lurching forward and shaking when we are stopped at a light or a sign. The rpm keeps going up and down rapidly, it tends to go away once we start moving, But if we are at a long light it will shut down the entire engine and we will have to turn it back on. Only 4 times has it done this while the car is moving.
We took the car to a mechanic and they change the fuel filter and told us that probably one of the major problems was this air pressure system, but cost $400.
Do you by our descriptipon that this will solve the problem (our mechanic isn't so sure because he really can't pinpoint the problem). Please, I need desperate advice before I invest on sucha pricy part, that might not even solve my problems. Thank you.