MAF if the revs are fluxuating so badly. Good idea NOT to floor it as it could lean the engine out if its sending wrong signals to the
ECU.
Fuel pump could also be a likley contender and would cause a pinging noise if its shat itself. Try cleaning the Mass Air Flow sensor with electrical cleaner and hope for the best, if its WORSE or a LITTLE better after you clean it chances are its the
MAF. If nothing really happens id say pump.