i have a 1981 toyota celica that keeps dying when you let off of the gas i have had it in to a mechanic who put in new plugs and wires as well as a new diaphram in the carb then he said it was sand in the carb it worked ok for 3 months aftereach time he had it then went back to doing the same all over again,i cleaned out the tank and blew out the gas line and put a new in line fuel filter on it but it still is not working, i want to know if my next step is to over haul the carb?