Suddenly little heat from heater. Very little hot air comes out, depending on OAT. Took ‘stat out functions as normal in saucepan. Acts like whatever turns hot water valve open, does not operate, some hot water does come through. Took it to local Mitsubishi dealer, replace valve body for $4,000.+, not worth that much. Said ‘wheelbarrow’ mechanics replace everything, no matter what. Tried all positions of controls.

Any way of reaching and manually operating valve?

Thanks.

 

It can be as simple as a control cable (or the cable cheating) from the temp control **** slipped off the little plastic tab vehind the dash. That will keep temp control gates in whatever position they were when that occurred. Possibility #2 is clogged up heater core.
I seriously doubt throttle valve body has anything to do with this issue. Cabin heat comes from the outlets in the back of the engine, nothing related to the valve body.
You can kind of check if the heater core functions by checking temperature of the two hoses that go to it. Under front the passenger frint side by the firewall you'll see two hoses going from the back of the engine and into the cabin floor. Warm up the vehicle until the gauge shows Normal temp. Get under the vehicle and feel the two hoses. One should be very hot (from engine to heater core), second will be colder, but still warm (return line). If both hoses are cold, that may indicate that coolant is not circulating properly through the heater core due to it being plugged.