If after cleaning out the hoses and cleaning all the air intake parts it's still playing up then i'd spend 50 quid and give it a proper mk3 service. New ECU relay, new fuel pump relay, new coolant temp sensor, new vac hoses, new ignition leads, new spark plugs, new rotor arm and dizzy cap. Do you have any dioagnostic tools? COuld be worth scanning to see if the crankshaft sensor has gone too