This happened to me, but since you mention no other symptoms you have to find them. My headgasket blew when IDLING... and caused an uncompressed mixture to be ignited - the gasket was torn between two cylinders. I doubt it is your problem, as you don´t mention backfire through and UP the air intake.
Remove air filter and get someone to see if petrol is injected. If not, check fuel pump, and filter.
Morten.