As far as the heater motor goes, open your hood and give the black air scoop a good bang with your fist (hit it near the top where it goes into the air box). If it starts running, then your motor brushes are worn out. You can usually get it to limp along by doing this for a few thousand more miles til you get a chance to change it out.
Also your high idle problems may be related to the Idle Speed Control Valve. You can check the the electrical portion of the ISC valve with an ohm meter. When you unplug the connector, you will see 3 terminals inside. Measure the resistance between the center post and the other 2 posts. You should see 18.8 - 22.8 ohms in both locations. If the resistance is not within this range, it is bad--Replace it.
If you haven't flushed coolant in the last couple years, now would be a good time to do it and it may help. I never use any kind of chemical products to flush, I just hook a garden hose up to a flushing kit tee, open the radiator drain valve, then adjust fresh water flow to match drain rate. Once I get the reservoir to maintain a constant level, I let it run for about 20 min or so. Then it's just drain and refill with new antifreeze. Here's a picture of where I put my tee. Tim
PS: All my Previas are naturally aspirated, so I may be way off base for those of you with supercharged versions. Tim