4crawler is absolutely correct.. You're going to see some drain. The way I wire megasquirt, there isn't any current to the ECU itself when the key is off and I believe the OEM ecu is the same, but don't discount that there isn't current going somewhere else - like to the OEM clock or aftermarket radio.

You really need an amp meter to figure out HOW much current you're drawing.

I need a pin out of the stock ECU to help you and my server seems to be down.. There are two pins on the stock ECU that get relay power - both should NOT provide 12v when the key is OFF.

If it's AFM related, my guess is that you're triggering fuel pump - maybe...