2000 Vauxhall Astra smoking under acceleration

hi there, i bought a vauxhall astra van back in april this year with a 'fuel in oil' problem. this turnt out to be the injector seals. problem solved. then it developed a miss fire like problem, turned out to be fuel pump timing was out. all this time it was pumping a white smoke out the exhaust. NOW it still 'miss fireing' under acceleration, and throwing up the engine warning light, causing the van to hold back enourmously. once the engine light goes out the van runs again properly until the next time you stop or slow down. im getting very frustrated now and would like a bit of advice, as to what it could be.