Heater work perfectly when running but does not work when id

When driving along the road the heater works perfectly. When idle or stopping the cold air blows out.
The temperature gauge shows close to the middle point between hot and cold. Even when it idle the temperature gauge still stays in the same spot. Doesn't go down and doesn't go up either. The problem I noticed is that even though the car is not heated up yet the temperature showing on the gauge are already up in the middle point. Care to give me some advice on what I should do. Got the heater core check out but found nothing wrong with that. No leaking and everything seems to work o.K.

I really don't know much about cars. All I know is that the car heaters work perfectly when cranking it up but slows down when it is not moving or when it stops at the lights. The temperature gauge remain the same whether the heat is hot or not.

I'm having the same problem with an 02 civic with 100k miles. The car idles normal (about 750) just as it always has, the temperature gauge reads normal right in the middle. When your going down the road the heater blows hot but if your coasting for a while (like down a long hill) it starts to cool off, and if your sitting at idle for more than a couple 5 minutes there is no heat at all. But if I'm stopped and rev the engine for 30 seconds or so the heat starts to come back. Oh and I haven't bled the ac system or done anything to the car since the problem has started.

I have the same problem with my Eclipse (2003, 75K Miles). I idle around 750, the heat starts to warm slightly around 2000 but to get it really hot it needs to maintain about 3000RPM.