Does anyone know anything about either idle air controls or vacuum leaks?

What is your question?

My 05 ford escape has been running really high rpms while in park. If I sit in park the rpms will go up over 4 and it makes a loud humming sound like when you accelerate quickly while driving. Yesterday was the first time it did this while driving rather than parked; it was like driving with cruise control on that kept getting faster. I did not even have to touch the accelerator because the rpms were running so high that it was just going. I had to be on the brake the entire time, and when I had to come to a complete stop it was hard to do so. This past spring I had new plugs and wires put in because I had a cylinder misfire. I asked my mechanic back home and he said possibly the idle air controls or a vacuum leak, but I don't hear a hissing sound like a vacuum leak would have? I'm worried mainly because I don't know if this is safe to drive or not. I can't get into my regular mechanic for a while, and I know going to the local Ford dealer will be much more expensive. Any ideas?