Celica :: 1994 GT - No Heat At Idle

My son has a 1994 Celica GT with the 2.2 5S-FE engine. Recently told me his heat didn't work very well, he had mentioned it last year but due to extreme cold we've been having I decided I would look at it for him. So anyway, I started by pulling the thermostat thinking it was probably stuck open or possibly someone had removed it completely, well there was one in there and it was closed so I tested it in boiling water, worked fine, replaced it anyway.

So then I checked behind and under the dash, thinking maybe something was opening or closing completely, but they are connected and operating, when I move the controls inside I can hear the doors moving and closing and all the linkages under the dash are connected and operating. Still no heat, so I figured the heater core was clogged since the return hose didn't seem to be getting hot, or the heater control valve was bad, pulled the heater core hoses, checked the heater control valve, control valve worked fine and was not plugged. Flushed the heater core, nice clean antifreeze, I then checked it with air, manual said put 6 psi on the input and make sure it was coming out of the return, which it was.

Reconnected everything, bled the air, still nothing, took the hoses off and connected the return hose to the heater control valve, bypassing the heater core, both hoses got hot. Sure seemed like a clogged heater core, did the air test again with 2 psi, still made its way out the return side. Reconnected everything again, still same issue, return hose never got hot. So while it was running hot with thermostat open, I removed the return hose, nothing coming out of the core, then I revved the engine and it started coming out, reconnected it and ran car at 3000 RPM, finally a little heat out of the vent, about 115 degrees by thermometer placed in vent, as soon as I let it idle the temp fell back to 80 within a minute or so.

Now I figured the water pump impeller was worn/corroded or was slipping on the shaft, so I pulled the whole thing apart. ( I should mention that the entire cooling system is very clean I don't see any corrosion anywhere) Any of you that have done this knows what a pain in the butt the whole job is, anyway, when I got it apart I was surprised to see that the impeller looked like new and was definitely NOT slipping on the shaft... what the heck???

When I took the pump off the housing I noticed the housing had a lot of wear, it look as if the previous owner let the water pump fail to the point that the bearing wore enough that the impeller ground down the raised boss inside the housing, I though AH-HA, this has got to be the problem, water is not actually pumping/circulating inside the pump as efficiently as it should, hence the reason I only get coolant into the heater core at high RPM. So i replaced the housing, the water pump, and while I was in there I did all the oil seals, and the timing belt. Well I got it all back together, fired it up added coolant, let the engine come up to temp, bled air, still NO HEAT!