I have a 2004 Jaguar XKR with 145,000 miles on it. I recently had the supercharger belt, serpentine belt, and oxygen sensors replaced. After the oxygen sensors were swapped, I noticed the car began to jerk upon deceleration. As I let off the gas it seemed as if the car was breaking every so often. I also noticed the car seemed to be struggling with acceleration. I told the mechanic that this issue began after they swapped the oxygen sensors (all four), but he told me it was most likely not the cause. After this, I swapped the spark plugs for the iridium plugs recommended here on the forum. This fixed an issue I was having where after 50 mph the car would vibrate in the right rear. Although it fixed the vibration, now the car seems to pulsate when trying to accelerate. You can hear the engine struggling. Is this yet another set of misfires? All 8 spark plugs were swapped, may they have become dirty from the previous plugs? Note, I also had the transmission oil swapped and the filter replaced. How should I go about fixing this issue? Any advice on the jerking with deceleration and pulsating on acceleration? Thank you so much!

 

You need to get the codes read to have any understanding of what's going on, otherwise you're just guessing and firing the parts cannon at it.