[Shadeyman]

Bosch MAF sensors have a self clean cycle, If I remember correctly the sensor wire is heated for about 5 seconds every time the engine is turned off. I'm sure the wire glows red, yes it does get that hot. While the heat it produces burns 99.9% of the crap that does find its way onto the wire, the stuff doesn't always fall off the wire, some stuff clings on causing false readings and in my case the "Engine Service Required" error. Using MAF cleaning spray helps to dislodge those stubborn bits of crap and return the MAF sensor to its former glory.

EDIT.
I've just attached a PDF document to this post. Its an interesting read if you want to know a little more about MAF Sensors.