Could be several possibilities none of which I may be able to eliminate:
1. Tune-up!  You are not getting enough spark or Fuel!  Plug-wires may be cross-firing or bad ground from body to the engine - run a new ground wire to engine from battery or body-ground.
2. Replace fuel filter or do fuel pressure test to determine if f-pump is weak or lodged with corrosion or dirt particles.
3. replace plugs and wires and clean coil-pack ignition module (where plug wires originate from) use a brake-cleaner or throttle-body cleaner but be sure fumes are evaporated and dry before starting or spark could cause explosion from fumes. Oil on module could cause spark to jump.  Do not run plug wires along each other or will jump spark, wires must be crossed once or twice for prevention of this.\
4. check all vacuum lines around engine - a cracked vacuum line can cause a lot of problems.
5. injectors may be dirty or bad - easier to replace complete intake from scrap-yard then to pay $100.00 for new injectors each!
6. Coil-pack on ignition module could be cracked and may need to be replaced.
These are only possibilities of course with the little info you provided.
Hope this helps.