Are these worth fitting to the TFSI engine? I fitted a set to my RS Focus and they made a big difference to the way it ran. It got rid of the misfire it had once tuned. Has anyone who has fitted them noticed an improvement? My car has a slight misfire, like some others have had on here. The reason I ask is that I am due to service my car, as its done 21000 miles now and has only ever been serviced once at 13000 miles according to the service book. I dont like the idea of leaving plugs in for 40000 miles and I am a big believer in changing them every 10000 miles. I dont known whether to stick to OE plugs or fit Iridium ones?

I've fitted a heat-range colder plugs to mine Matt, made a slight difference - ran smoother if anything.

Thanks Harry. Im going to purchase some and give them a try.