About a year ago I purchased a 2017 Mustang that had been modified by a local speed shop. When I first begin driving the car I noticed that the car engine would surge at idle after being driven for 30 min or so. I didn't think much of it at first. Fast forward 6 or so months I noticed that the that the ecu was setting system bank 1 and 2 lean.
The drivability of the car begin to worsen, after a 30 min drive it would begin to misfire at idle with ipc a/f readings in the 15-16 range just before the misfire started occurring. I figured "ok, I need to find out what's wrong with this engine." I grabbed a can of brake clean and sprayed around the top of the engine and realized that the supercharge to cylinder head area on the drivers have had a vacuum leak. So I put off repair the car for approx 2 months. If I would have only known then what I do now I would have fixed it that day! I finally had some free time and pulled the lid off and what I found was shocking- I found the vacuum leak which was a super charger bolt was missing. My first thought was ok the speed shop was a joke and left one out. I quickly realized just how lucky I was because 2 runners over I found my missing bolt! just sitting in the runner, I was not wedged either. I used a magnet to remove it. I found each and every both lose. So I removed the super charger, installed new seals and added a little dab of blue Loctite to each bolt and went through the torquing sequence 3 times to make sure that it was fully seated on the intake flanges and no bolts were lose. Afterwards, the car runs great! All this makes me wonder what the tune is like though. I have over 25 years experience in the auto repair field so dealing with PIDS, data lists and data recording is not a problem just need to learn the software and and what and when to make changes. Thanks and sorry for the long winded post.