For the past couple of years I have been chasing an intermittent Restricted Performance issue that usually popped up when I restarted an already warm engine. It never would throw codes but occasionally would run a touch rough for a moment before settling down. I thought possibly coil pack or throttle body related but it was difficult to troubleshoot.

Last year I finally caught a P0121 TPS and posted this https://www.jaguarforums.com/forum/showthread.php?t=96436
I cleaned the contacts on some cables and made sure the throttle body was all clean in the process but still had occasional issues. I thought I might have to spring for the gold contacts per the TSB but it wasn't bad enough to warrant it yet.

This year after hibernation the problems increased dramatically. Every time I attempted to restart a warm car it would run rough and throw restricted performance. It finally threw the P0175, P0307, and P0357. I was originally going to order a coil pack straight from China but since the problem was getting so bad I didn't want to wait that long and ordered one off eBay.

The car is at 82000 miles and between running rich when cylinder 7 started misfiring, I decided it would be a good time to do plugs as well. I used some Bosch iridiums and was surprised how worn the original plugs were.

It's been a couple of weeks now with the one coil pack replaced and new plugs and no restricted performance, rough running, or any issues. The car runs like a dream and it appears to have picked up a few mpg too. It goes to show how touchy these Denso coil packs really are and how they can be tricky to troubleshoot until they are almost completely dead.