[autoque]

I've got a N52 motor in '08 X5.

Before I arrive at a destination I usually turn the AC and the compressor off and turn the full heater on in order to dry the hvac system. I set the temperature at the highest setting both by turning the knob and going in the idrive setting, so basically it's the hottest setting you can have.
What happens then is when I'm stationary, I get a rough idle. It goes away if I give it gas. Any idea what's causing this?
By the way, I've replaced water pump and thermostat a couple of years ago and the problem existed before then, and still after. So it's not the WP and thermostat. The MAF sensor was also recently replaced, but no effect.