1994 Ford Explorer

My 1994 Explorer starts up good and runs fair for a cold motor for about a minute or so then the check engine light comes on. As soon as the light comes on it starts to run rough and hesitates when accelerating and pops and backfires when accelerating hard. I have only had this vehicle for a week but can tell that there has been little or no maintenance done and probably has dirty injectors, carbon deposits, old plugs etc. I put some fuel system/carbon cleaner in this morning but haven't driven enough to expect any noticeable improvement. We disconnected the harness to the mass air flow unit to see if it ran any different (it did) when we plugged it back in and wiggled the harness the engine smoothed out for a while but went back to running rough very quickly. I bought a spray can of cleaner for the mass air flow sensor but it is too rainy out to use it. What do you think about the spray cleaner stuff, does it usually work or not? If the air flow sensor is not the problem what are the next most likely suspects to check out. Thanks for any help you can give, I am out of work and I am currently living in this car.