It might also be the inlet manifold swirl flaps. if so, it needs urgent attention because they could break off and be ingested by the engine.

The standard cure for a dirty air flow meter (this month's 'Diesel Car') is, while stationary, to have the engine warm (from a run), let it idle for 15 seconds, then gradually build the revs up to 2000rpm, then immediately switch off. That signals the ECU to commence a self-clean programme of sending a high electrical current through the MAF's platinum wires that burns off most hydrocarbon deposits.