when i am at idle my heat sucks, but once the rpms go up my heat gets nice and hot. i thought that the water pump was weak so i replaced it and the themostat with it and i tried flushing the heater core out and nothing changes. does this happen to anybody else.

 

You have air in the heater core and probably sediment and crap too. Core needs to be flushed and burped, and replaced if that's not a fix.

 

the OP says that he had already flushed the core.

 

True - sorry, what I shouldve said was the core needs to be flushed using burning hot water and CLR. There were a couple other heat-related posts last night and I mentioned this in one of those. I should have been more specific here about that.

 

How does one "burp" the heater core?

I think I have the same problem in my 1999.5 2.8 B5.

 

pull the car on an incline, and start it with the coolant tank cap off. When you start it make sure the heat control is to its maximum temp and let the car warm up. This opens the heat valve for it to circulate and the incline lets the coolant tank be the highest point for any trapped air to escape. This on my bmw was a pain but not so much the a4, fill if needed. Also while its running massage the coolant hoses helping any trapped air out. This will take a minute since the thermostat needs to open to actually get coolant circulating through the heater core.

 

Thank you, Dozanti, I'll give this a try. I think I'm also going to flush the heater core with CLR.