My 1999 Honda Odyssey idled erratically a couple of times a few weeks ago while in park. Fluctuacte from 1000 rpm to 2000 rpm. I turned it off and back on and turned the a/c off and on. It stopped. It did this again with my wife and she simply revved the engine and it stopped. There is no CEL coming on or any maintenance lights. Van has 226,000 miles. Is there any way for me to figure out what's going on? Or should I even worry about it?