the mas flow sesor is a sensor not a valve, if it is dirty it can cause promblems as well if the throttle body is dirty. use mass flow cleaner on it not carb cleaner ! the problem of the truck running bad when you start woith the pedal to the floor is the computer ecm go nuts trying to figure out what went wrong.

I would replace the fuel filter, clean the trottle body, the mass flow sensor but be easy on it or you will damage it! replace the plugs it not done lately.
? do uou have a high low setting on the fan ? if it is always on high it could be cooling the engine to much.

John