93 Eurovan Idle Problem. Thermostat housing needed

My 93 Eurovan has 122000 mi on it. I have a problem with it stalling intermittingly at a light when it is under load (air on) the idle speed drops from approx 800 rpm down to 4-500 and then comes back up and sometimes it just drops off to "0" I have new fuel pump, plugs.wires. cap and points. Tank removed and cleaned. Also cant find a plastic thermostat housing that is cracked.

Dealer is the easiest option for the housing. Try cleaning the throttle valve with throttle body cleaner & a toothbrush.