Originally Posted by Master Yodub
I was figuring it was a radiator problem because of where he noted steam in the engine bay. If air got into the system through a leak in the radiator, it could cause his funky idle.
Those "possible causes" I listed are for the CEL (P0505). I thought he had two separate problems, the cel and the radiator. But yes it sounds like he has the notorious radiator leak problem. Rather strange to me how he had a idleing problem, got the CEL and then the radiator gave him problems. That's some bad luck.