MAP or MAF? And does it need maintenance?

The MAF sits between the air cleaner and the intake manifold. Its purpose is to measure the amount of air coming into the engine in order to mix the proper amount of fuel. As such, it is an extremely important component for efficient engine operation. I would also imagine it is quite delicate. As far as cleaning, it would only be warranted if the engine is running rough, I'd say.

 

If I were going to clean mine, I would only use a specifically marked MAF cleaner. Any residue that might adhere to the "hot wire" section of the sensor will affect its accuracy. Could even make its performance worse. Good guidance though to not fix what isn't broke. MPG decrease or engine performing roughly are clues. Could be other things too (air filter, plugs, bad gas).

 

The MAF can appear defective when only the air hose is loose -- since it detects air flow. After 60K miles an Engine Check Light code showed a fault in the MAF. The Mass Air flow meter is attached to the intake air cleaner. The air cleaner had just been replaced. Dealer found the intake hose loose and repaired at no charge. Dealer also said MAF replacement very rare on Prius compared to other cars. The sensor is the same type used for servicing building air conditioning vents, a hot wire anemometer. Temperature of a heated wire is measured by a thermometer with wind cooling it off. They work on low velocity flows compared to weather fan based meters and avoid moving parts. Dirt in it or baked onto the wire can distort the readings. There is special cleaning fluid for it sold in stores, but it cannot be rubbed due to delicate wires.
Air flow is measured on all modern computer controlled engines to adjust injected fuel mixture. An abnormally low temperature from dirt blockage etc. can be used by software to detect faulty measurements and turn on the engine check light.
The Check Light dumps too many things onto one indicator as it includes loose gas caps as well. Autozone stores, for one, will read the error codes for the specific fault detected free of charge. It seems with the MAF code, the unit needs inspection for the hose etc. before doing anything.

 

The Manifold Absolute Pressure (MAP) is located very low in the engine compartment, on the intake manifold, next to the throttle body. But I doubt your mechanic is going to clean only the MAP without at least doing the throttle body while he's down there.

Just to be clear: There is a MAP sensor, and a MAF sensor. Your mechanic is probably offering to clean the MAF sensor, which is really easy to clean.