Are there any Range Rover technicians out there for advice please?

I have a RR vogue (x) reg. Has 24329 miles on the clock (valid) I have a message on the computer which I cannot get rid of. I booked it into a garage & they connected it to the computer & there is a fault on it (P1319) apparently this is a 'mifiring' fault. It drives perfect. How do I solve this without paying �90.00 per hour @ Land Rover?