No heat while idle

no heat while mini van idles it heats up while driving

Does the heater fan run? Is this a manual type system or one of those automated systems where you can set 68 for the driver and 75 for the passenger?

I would be looking for a vacuum problem or maybe a problem with air in the coolant or even a water pump.

Low coolant level. Add coolant, burp air from system, enjoy heat.