Hey 300! I think I have the same problem you're describing.For those who want to fix the problem, here's what to do.
Open the FOB by prying the 2 halves apart, after removing the key, then, using a jeweller's Phillips screwdriver, push down hard on the screw head before turning the screw: IT IS TIGHT.
Once opened, remove the battery, and using contact cleaner, clean the tiny gold contacts.
On mine, the tiny cupped disc that shorts out the 2 gold contacts when pressed, was loose and moving around, causing the engine to start on its own; I glued it back on with silicone rubber, and the problem is fixed.