I have a USA 2011 XF Premium 5.0L which has just on 40k miles.

I've started to get 300 errors with 2 or more cylinders, so I'm trying a few things to rectify it:

• Added fuel injector cleaner to the gas/petrol to give the injectors a clean to see if that helps.
• Trying to replace the spark plugs.
• Maybe will check the fuel filter if all else fails.

I'm trying to remove the passenger side rubber shroud that covers the cylinder head ends, to get at the spark plugs, but for the life of me, I can't get it off. Seems it's jammed tight against the side liner of the engine bay right at the last plug (closest to the engine bay) and won't budge.

Is there a trick to getting it off? It seems to be caught between the last coil and the side of the engine bay, Could the motor have dropped slightly (deteriorated engine mounts perhaps?), or what?

What seemed like just a challenge (due to tight engine bay), seems almost impossible right now.

Any other advice on what to check for 300 errors (300, 301, 302, 306)?

I have purchased to NGK iridium plugs and checked the gaps. Do you recommend putting copper paste on the plug threads prior to installing?

Thanks in advance for any advice. guru's.