I cleaned my IAC valve about a week ago or 100 miles ago. The check engine light has now come on. Could this be due to the battery being disconnected and the computer "rebooting".
No...battery swaps or disconnect has never resulted in a check engine. Do you have a scanner? If not, get one that provides a description of the code. Auto parts stores will read your light for free. Re-check any electrical connections. Did you "clean" any sensors?