A new AFM for one of these things is around $720, it would be worth your while and going down to Dick Smiths or similar and getting some contact cleaner and undoing your air filter box and giving the little electrical element that sits in the box behind the filter housing a spray, it's probably just picked up some dirt whilst sitting around.

My AFM did the same thing just after my conversion and from then on I made it a habit to spray it every 3 months, it lasted about 5 more years before the plug died and I had to replace it, it's about the only thing on my car that has let me down.