Looks like this (this is on a C5) on the right-hand hose, coming out of the airbox with the electrical connector on it.
Click for larger image.
Try disconnecting and cleaning the electrical connector first (contact cleaner, not WD40) as they don't usually just die but have a gradual deterioration for a while.
This is one after loads of muck and water were sucked in to the induction system due to a missing wheel arch liner in winter - needless to say it was cabbaged.
Don't touch the two wires or drop the unit, they are very delicate.
You can try cleaning the wires with either carburettor cleaner or dedicated MAF cleaner.
(a 307 110hdi) cruising along at 75 on a slight incline yesterday when it suddenly lost about half of its power, no warning lights, nothing, pulled over, turned off, had a look under the bonnet 
like ya do, it looked just the same as it always did 
started up and carried on still only half power but as long as there was no hills I could get it up to 70 again 
I will be looking at it tomorrow so here's hoping it is that simple 