try this 
function fbiscript () 
      local x, y, z = getElementPosition( source ) 
      rancher = createVehicle ( 490, x, y, z+2 ) 
end 
addEvent ("fbi", true) 
addEventHandler ("fbi", getRootElement(), fbiscript) 
  
--or 
  
function fbiscript (thePlayer) 
      local x, y, z = getElementPosition( thePlayer ) 
      rancher = createVehicle ( 490, x, y, z+2 ) 
end 
addEvent ("fbi", true) 
addEventHandler ("fbi", getRootElement(), fbiscript)