Now that I've fixed all of the problems that were causing fault codes and turning on warning lights, I've started to pay attention to the less obvious stuff. My biggest worry right now is that there seems to be a lot of backlash in the drivetrain. If I'm driving in traffic and I take my foot off the gas to slow down, then step on the gas to speed up, there's a noticeable jolt when the power from the engine hits the wheels. It's not a normal jolt, it feels like there's some play in the drivetrain. Hopefully it's not a transmission issue.

My first thought is that it might be engine mounts, but I honestly have no idea. What are the symptoms of faulty engine mounts? And what else might be causing a jerk/thud when going from braking to accelerating?

 

Does it what happened when coming to a slow rolling stop?

 

I have had my engine mounts broken and replaced in the past but I have a high mileage car. But it's not inconceivable that a car with as much power and torque as the XKR 5.0L has would tear through motor and/or transmission mounts. It's a good place to start looking.

 

No, it only happens when I go from slowing down to stepping on the gas. It can happen at any speed, but I don't recall noticing it when coming to a stop.

 

I play in the drivetrain would be an exceptional situation... but you did change the e-diff..
Perhaps you're feeling a 'clunk' in the transmission?? Though a fluid change helps, a ZF repair depot can really smooth out the jolts and harsh shifts..

 

Open the hood. Put car in drive with foot on brake. Hit the gas a little. If the engine moves, then you may have a broken motor mount.