| I can't find anything on stepper motor problems for that car, the only one that I know of is for the stepper motors being a little noisey.
For the heat fluctuation, as EXtech said, it could be an auxillary water pump (which is used to supply the heater core with hot coolant).
It may also be the heater valves sticking, or not functioning properly.
Is the engine running at normal temp, and is the coolant full?
It could be a control module problem as well. You'd really need to have it checked out to make sure.
For the airflow, EXtech is right about the filters. That's the most likely cause of low airflow, assuming the fan is running fine.
There are 2 filters under the hood that are easy to get to, built into the hood at the firewall.
There are 2 more inside the car for recirculated air, which are harder to get to. You'll have to remove the panel under the steering column, and also remove the glovebox. The filters are located on each side of the ac/heater case. | 
