I just got done re-doing the vacuum lines to my hvac system, and I just put a new heater control valve in.

The heater works just as it should... except at idle when I'm stopped. When I'm stopped at a light and the engine is idling, the air gets gradually colder and colder until I either start moving again or give it a little rpm.

The coolant temp is staying rock solid at about 190, and does not change when the heater starts blowing cold. The whole coolant system is topped off and leak free, and there is no air anywhere. The motor has always taken a little longer than usual to get warmed up in the mornings, do you think the water pump could be on its way out..?.. to where it doesn't flow enough water at idle rpm to circulate enough through the heater core?

any input is appreciated

when was the last time you flused the system? I would do a complete flush, and reverse flush, until all the water comes out clear. Then top off your system 50/50 with coolant/water. This happened om my 71, but a thorough flush solved the problem. Good luck

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This indicates poor waterflow through the heater core. Clogged core, restricted inlet/outlet fitting(s) at the engine and water pump, clogged hoses.

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