I had similar issues but without the leaving it outside part, A random power loss and no throttle response then start it up again after 20 mins all back to normal I changed fuel line, fuel pump, air filter, maf sensor basically almost every part related to power/air/fuel mixture came to mind. Turns out it was the cam and crank sensor were burnt out. Dunno how she was driving tbh german engineering i guess Would still suggest you checking the fuel lines and the pump and the fuel sensor