The unstable idle wasn't the problem that the throttle body was addressing. The problem was surging idle and stalling and it was definitely fixed by the throttle body replacement. (If it didn't, the dealer was more than willing to put the old one in.) The unstable idle seems to be worse when cold, and quiets down considerably when the engine is warm. I think it's a totally different problem. I'm trying some Techron to see if it helps.