94 sentra problem

I have a 1994 Sentra XE and recently it just started acting up. It started shaking way too violently and whenever I accelerated it shook a little bit and sputtered before actually accelerating. I replaced a bunch of things liek the O2 sensor, air filter, fuel filter, rotor head, and the distributor cap. Then I changed the mass air flow sensor and the shaking stopped but it still accelerated slowly like it has no power. I think it has something to do with the air intake but I hav no idea. Also the exhaust seems to come out peppered so to say not a constant stream of air. Hopefully one of you can help. Thanks.