No heat when van is in idle, heat works fine when van moving. 2001 Windstar

Water pump fins are worn . Not moving enough coolant at idle .

Weak water pump will do that,or a partially pugged heater core. don-ohio (:^)

check the trans fluid ?can you here the van go into gear or not at all ?

that could mean that your water pump impeller is broken. when you press the gas the remaining piece of the impeller is pushing the water and it actually makes it to the heater core. at idle it isn't spinning fast enough. ask a local autoparts store if the impeller is made of plastic.

If the idle speed is wandering, check the idle air control valve and the throttle body for dirt and varnish. The computer regulates the idle speed by the valve.

clean heated MAF, mass air flow sensor heated wires to remove varnish coating that leans out mixture. Do not touch wires. On big air intake tube.

Check the coolant level. If it's low, what you describe will happen. There is not sufficient coolant to flow through the heater core at idle. At 60mph the water pump is spinning quickly, managing to get some coolant through the heater core, so you get heat until the rpm's drop at idle. If it is due to low level, keep an eye on it to see if it drops again, as you may have a leak.

1st check your coolant level, if it's low, it will cause exactly what you describe. If the level is ok, post that info here, I'll help further.

Blend air door may be stuck. I removed a pencil from a heater box before. It had fallen from the dash, down through the defrost vents and jamed the door.

Auto transmision belts are shagged could be expensive