My A4 don't heat when I am on idle

[walouigi]

Hi Guys,
My car is A4 1.8T 2003
Lately I had to change my heater sensor as I had a check engine lights and the diagnose was TEMP too low, where I would start the engine and the fans for the A/C would start to work, it was going for about 5Min and then stop by itself. The car was at that time warming normal from inside, until I changed the thermostat, and the heater sensor, now all the lights are off, however, the heat inside the car will be warm only when I am driving and the RPM is more then 1300/Min. If I am on idle or even at very low speed (traffic) my air inside start to get cold. I live in Montreal so it is pretty cold out here, I have the climate control temp to 23C. I don't know now what is the problem, I just did a full engine flush yesterday, and this morning I still have the same problem.
Also 1 question, do you put the fan on auto or economy. I used to have the auto all the time, and it iwas warming, now on idle the auto get me a very cold air, the economy a bit warmer.
Any help will much appreciated guys, I read that it might be the heater core, or some flaps problem can you give me your thaughts on that, as heater core is really trouble.
Thanks in advance
walouigi :confused:

[towcestervag]

check water pump circulation
did you bleed cooling system correctly from heater hose near bulkhead the one with the pin hole

[walouigi]

Hi,
Thank you for your reply, actually it's no me that did the flush, it is my mechanic, and he told me he did a full flush, I will check with him on that.
Today I did a test , where I have put the auto to 23C, and I was on idle, then I started to press the gas, and got to RMP 3000, for about 30Sec. I noticed that the fan speed did not start to lower the speed when actually I felt that the ambiance inside the car was warmer then that. Can it be that the auto is not detecting the heat at all, and there is a problem with the new heater sensor or the thermostat that we have just changed?
Can you please also tell me where exactly is " did you bleed cooling system correctly from heater hose near bulkhead the one with the pin hole that you are referring to?
Thanks