1992 Range Rover Gasoline in oil, will not start

I have a rover that does not start. I had a mechanic have me change the oil and he was able to get the car started. There was gasoline in the oil. After the oil change the truck ran great for awhile. Then it stopped cranking. I checked the oil and once again it had gasoline in it. The mechanic told me that the idle air control valve was sticking and this was the source of the gas in the oil and the hard starting. This mechanic is reputed as being one of the best, but I am not sure I buy his diagnosis. Any ideas. All of my trouble started after running out of gas once. I have had starting problems ever since, and now fuel in the oil.