Heater blows cold at idle

i have a '07 3i when the car is warmed up it blows cold air at idle with the temp set at full heat. step on the gas a little and it starts blowing warm air. Ii took it to the dealer and of course they told me that this normal. I live in MN and its like 10 above zero to around -5. I know thats cold but the car should still be able to keep up. My old '98 escort has no problems. At first I thought it might a low coolant problem but thats full. Has anybody had this problem and have any solutions? its a 3i with a 5 speed.

check your antifreeze level.  its prolly low.

I've noticed the same thing this winter when it is 20 F or lower.  At stops, the air is luke warm, but the instant the rpm's come up, the air gets hot.  I would assume that this means the cooling system is working very well - which is good.  I would also guess that if I decide I need hot air at idle, I would need a hotter thermostat???