I have a 2007 Sequoia that idles rough after it warms up. It overheated when I lost the radiator and I have had the problem since. The oil looks fine and I dont have any vapor in the exhaust. When at a stop in drive, the idle seems to vary between 5k and 7.5k rpm. At 5k the engine runs rough. At 7.5k it doesn't run rough. At a stop it will alternate betweeen 7.5 k and 5k rpm. any thoughts?