Toyota Repair: idle reving up and down

Question
2002 Tacoma, 4wheel drive, 2.7 liter, standard trans., 124000 miles.

I recently spent all the money I had buying this vehicle. By the time I put 400 hundred miles on it, it becan reving up and down 2000 rpm to 1000rpm when warmed up. When I start it it stays on high idle- 2000rpm. Can't get it to lower rpm idle.Cleaned the throttle plate and intake. Cleaned the idle control as best I could from inside the thottle- didn't have the special screwdrive to remove the screws from the throttle body. Checked all the vacuum hoses for leaks and the MAS. Stumped, as is my mechanic. The check engine reading was p0505, I believe. Got any hints for whats next? No rust so I don't think it is the ground.
I don't have money to throw parts at it. Is it safe to run while suffering this problem?

Answer
Hello, you are getting the P0505 because of the idle fluctuation, to be sure I would remove the throttle body and then the IAC valve for inspection and either clean or replace it depending on it's condition. Check to make sure the engine does not overheat, this can also cause idle fluctuations, if the IAC does not cure the problem try replacing the engine coolant temp switch, be sure the PCV valve and the hose is good.