I have a 99 Ford Taurus with a 3.0. I recently replaced the water pump because it was leaking. The heat worked perfect before that. Now iafter I replaced it it blows cold air when you are idling. When. You are raising the rpms it will blow warm air. I burped out the system, refilled the coolant. The coolant looked rusty so I flushed it out. And still nothing. The car has not overheated. There are no leaks. I was thinking it might be a clogged heater core but I think that's a little odd that it worked fine before I put the pump in. But I've been wrong before. Any suggestion on what to do or advice would be greatly appreciated.