If all the other suggestions don't pan out, locate the idle air valve and give it a good smack on top with the flat side of a good sized ball peen hammer. I used to love doing that to clients cars in the old days. I never did charge for the acquired knowledge of knowing where to hit the engine. Seriously the air valve is made of two pieces of aluminum that walk apart from heating and cooling so many times. If it has separated some, a good hammer smack will move it back and bring the idle right back down.
Auto Zentral Ltd.