I keep thinking this has been answered before but I can't find it. I've searched everything from "Check Engine Throttle" to "Coast Engine Light."

Anyhow, driving at a slower speed ~40mph, (though it may happen at other speeds, I only noticed it at this speed) whenever I left off the gas to slow/stop and start coasting, I get the Check Engine light. It happens right around the 800 rpm mark. It goes away if I apply some brake or more throttle.

Anyone know why this happens?

EDIT: I don't get power surges or anything, just the light, everything else continues working fine.