please help me diagnose these three problems!

[sd88supra]

1. Unstable running engine. When stopped, the RPM needle never stays at one, but goes up and down around it. You can feel and see the engine sort of "rev" itself a little rhythmically. I had my mechanic see it but he said hes gonna have to do a full inspection and wont be able to get to it till next week. He has ruled out a tune up and says it could possibly have something to do with a bad catalytic converter. The idiots at Firestone had told me it was "using reusing old fuel" but I dunno how reliable they can be since they did after wreck it in the first place. So, for those of you experience Supra owners, I was wondering if any of you have had similar problems. Mines an 7GME w/ 108k original miles.

2. I cant get the damn high beams off! This is the second MK3 which I have a problem with. Seems the light swtiches were made so brittle. Is there anyway to have them be sturdy?

3. If the car is moving very slowly (like in heavy traffic) the car gradually heats up, and when I take off again the temp gauge quickly goes down and then becomes unstable. Thermostat change?

I will be using it as my commter car for the next 3-4 days, about a total of 10 miles a day. Am I safe?

one last question: 7MGE uses 159 or 169 teeth?