On my mac air late 2011 I;m having a power problem

Hello,
About a week ago a small amount of coffee was spilled on my air. I quickly powered off and turned upside down as I dried the keyboard. It was really a small amount and after I finished I powered on and all was well. That is until about 10 minutes later, now if I'm not typing or moving the mouse I get a pop up screen asking me if I'm sure I want to power down, giving me the option to shut down, sleep cancel or restart. This happens within 15 seconds of my not typing or moving the mouse. If I hit cancel I can continue using the computer until I stop again for approx 15 seconds. If I don't hit cancel it will power off. Everything else functioning correctly. I took it the apple store and left it for a couple days, they called and wanted $783 to repair. They said they would be replacing everything and it would be like a new computer. Needless to say I didn't that, since I'm typing this on it right now. I tried to reinstall the OS but even during the reinstall if I don't move my finger on the mouse pad it will power down. I did get the install complete but still have the problem. Anyone have any ideas, or is there a way to prevent a shut by disabling something? Thank you in advance for any advice. PS I popped the power key to see if something was under it causing the problem and there wasn't anything and it didn't even look wet.