1990 Other Plymouth Models mass air flow sensor?

Just purchased car (1990 Plymouth Laser RS 2.0 4 cyl.) And was told it has been sitting for a couple of years - Starts right up and runs well while sitting but once put into gear it runs bad and boggs down and sputters with low idle and has white exhaust smoke - check engine light is NOT ok, engine sounds great and only has issue when driving. Mechanics checked head gasket (most likely item with white smoke) and does not believe the smoke is from a bad head gasket its from oil leaking into the exhaust and thinks it is either Mass Air Flow Sensor or something else making it run poor - trying to avoid spending more than the car is worth replacing everything could possibly be - any thoughts?