how can i fix my van, corsa, 14v,combo?

my van its petrol as well as LPG (liquid petrolium gas), when i started it, it started going up the revs from 1000 to 4000 then back down and up again all the time, and my foot wasnt on the gas, then i had to drive home from work and as soon as my put on the clutch the revs would go up even higher i drove the whole way home eithout hardly using the gas because it was going on its own and to brake was even worse because i was braking and the van was trying to accelorate. does any know whats wrong it