'90 Toyota Camry V6 LE idling low.

My 1990 Toyota Camry V6 LE, among other problems, is idling around the 500 - 600
rpm range whenever stopped. When I gas it up, the rpm returns to normal. I don't know
what is wrong with it. I hear that Camrys tend to have a stalling problem, and want to
figure this out before that happens. It could be the IAC (Idle Air Control), but, again, I
don't know. I don't have enough knowledge about cars to figure the problem out myself,
and don't have much money to be paying a mechanic to fix it...I feel they will clean me
out, or more. It could be the temp gauge, for all I know.
I also have to replace the thermostat, and most likely the lower radiator hose, if not the
water pump (most likely my leak is coming from the hose itself, right at the connection
to the water pump); but, I don't think either of those problems have much to do with the
car idling low.
What is the most likely problem?