For those DIY types, I spotted this on Amazon today. I hope it's ok to post the link. I have no affiliation with the seller. I've seen this product typically selling for $50+.
There is a coupon for $10 off you can click on the listing and an additional rebate from 3M (if bought by 12/31) for another $10. Net cost to me $17.

 

3M make pretty good stuff cant comment further

I do remember reading somewhere that you cant clean the throttle bodies on the XJ8 not sure if that's true on the X350 or if its the X308

I would ask around on the forums first you don't want to kill the throttle body its expensive