2003 Jag S Type will start to buck and lose power when I accelerate with anything but a feather light touch on the gas pedal. I get a 'restricted performance' readout on the LED. If I let up on the gas (i.e., stop trying to accelerate) the problem goes away after a few moments - so far.

Any guidance would be helpful

 

First this is the x308 forum and you will probably get better help post in the x200 forum which is correct for your vehicle.
The bucking is cause by the restricted performance to help prevent further damage to the engine. You need to get the DTC codes read and posted so we can help you sort out the restricted performance. I would limit driving to as little as possible until you can get the codes read and the problem diagnosed and corrected.

 

Chances are it's misfires and/or air leak(s). Don't keep doing it or it'll be very expensive. And try the right forum then use Search / read posts about these issues.

 

My money is on the fuel pump. Check the fuel pressure. I had similar problems, and monitoring the fuel pressure while accelerating showed a drop in fuel pressure. It was fine at idle and light throttle.

 

+1 Mark