if you have done all diagnostic tests and all seems ok go back to basics. check electrical connectors, for breaks or damage, has the condition of the exhaust system been checked ie blocked catalic convertor, or muffler system , check all vaccum fittings for condition ie perished hoses ,check all ported vaccum fittings, gheck throttle and choke linkage for ease of movement, is the choke adjusted correctly , or is it damaged