could be off timing, it could even be the fuel injection system, there is alot of things that could be wrong with it... to me it sounds mis-timed, but that's just my best guess. did you change any belts or even take any off, yourself right around the time you noticed this problem start? or mess with the distrubtor/spark plugs/spark plug wires? did you change the spark plugs recently? if so were they properly gapped? anyone that could tell you what's wrong would need a bit more information then what you've provided.

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