Plugged EGR passage which restricts the flow of exhaust gasses, faulty EGR solenoid, faulty EGR solenoid wiring/harness, vacuum lines damaged or disconnected to the EGR valve solenoid or to the EGR valve, or a faulty EGR valve.
I know that on a 1995 it is located in the rear driver's side of the engine compartment. Although if you just follow the fuel line (it should have a flow arrow on it) from the engine block out it will run into the fuel filter.
Trouble code P0400 means:Exhaust gas recirculation-flow malfunction
EGR Flow malfunction
P0403 = EGR Flow circuit malfunction.
I would look into a stuck open, or jammed Egr Valve.
It could be a tear in your air cleaner hose. The hose from your air filter to the throttle body. If the mass air flow sensor does not have enough air suction ( or enough volume of air) going across it it will shut down the engine.
Trouble code P0402 means: Exhaust Gas Recirculation Flow Excessive Detected
Just because a code that is titled to a particular system is noted does not mean that component is bad. Check the passageway.
My book shows it to mean: Evaporative purge flow sensor fault.
change the egr valve
Dealer needs to prove that the flow-master was the cause of the malfunction...
where is air flow relay on 2000 ford windstar