The map sensor is also used for egr activity confirmation by the ecu, its not just for egr though,

Before start, its used as the barometer by the ecu and after start it is used in conjunction with the MAF sensor to create a correct engine torque/load signal which is used by the engine ecu and also used by the tcu and esp.

Replace it, its pretty cheap, however if you find that the vacuum hoses are perished, toyota dealers sell genuine hose in 1m lengths, and if the small vacuum chamber in the manifold isnt holding vacuum you will need to install an external vacuum tank or a new intake manifold.