A/C and heat issues

There is no restriction of air, the flow is always consistent. It is just the temperature that is inconsistent, and being that I am having the same problem with the heat and the A/C I though there might be a common denominator. So basically the word heat and A/C are interchangeable in this problem. At idle little to no AC/heat, at 2,000 to 3,000 rpm all is good. Whether I am traveling down the road or at idle revving the the engine in the driveway.

Thanks.

I am fairly mechanically inclined and have checked most of the obvious problems. I am surprised to hear there is no common denominator between these two issues. My guess would have a head gasket or some odd vacuum problem. But I will keep looking. Oh, one thing I did not mention is 90% of the time you turn the climate control system on or off there is a kind of banging noise, like a wooden spoon against a plastic bowl kind of. I thought it was a vent attempting to open or close, but again I found no issues with airflow.

Thanks again,
Mike