Ok, So I have a 88 Dodge Caravan. The heat only works when I Have my foot on the throttle. When Im parked I have to hold the throttle too 2500 Rpms to get heat. The Second I take my foot off the pedal Its instantly cold.
Now I have to vacuum lines coming out of the firewall about mid engine. One of them goes to the Break Booster. The other one I cannot find a home for. I have checked vacuum diagrams and everything seems to be right. I have searched for a spot to hook the left line up to and cant seem to find anywhere to put it.

Any thoughts

matt

 

I had the same problem on a 94 Caravan, Simple fix, change the Thermostat. Canadian tire ( My local all purpose shop) sells them for around 20$ its easy to fix, its located on the engine where the big Radiator hose goes in. When i put a new one in, Fixed the problem instantly. you can also get thermostats rated for diff temperature depending on how much heat you want.

 

I'm not sure if you have the 2.5 or the 3.0 but the 2 vacumn lines come out by the heater hoses. One is black and goes to the brake booster, it is the vacumn supply to the heater controls. The other is gray and goes to the water control valve, a vacumn controlled valve in the heater hose and is used to stop coolant flow through the heater core when you have selected max a/c. Usually when you have no heat at idle, the coolant is low, you could also have an issue with the water valve. You should be able to follow the heater hoses with your hand and see where they go from hot to cool.

 

Mine did the same thing,replaced water pump and thermostat.That fixed it along with flushing !