So I jacked the front end of my XK8 off the ground, one side at a time and slipped a couple of 2X8s under each front tire to give me a little extra room to change the oil. After I completed said oil change, I left the car raised to check for leaks, started the car and Bam, idles horribly. Restricted Performance indicator lit up and eventually the CEL came on and so I pulled the P0300 and P1316 codes with my reader. There were no issues with the car prior to this...dang. Accepting any advice, sympathy already presumed. Thanks.

 

I would get back underneath it and check to see if by chance on of the O2 sensor wires has been damaged. P0300 is random misfire and P1316 is excessive emissions. It may be coincidental but I think you have an upstream O2 sensor failure. I will take a look in JTIS and post which bank P1316 indicates and get back to you.

 

Secondary cam chain tensioners. Have they been replaced ? If not, you could be in for an unpleasant surprise.