Q: restricted performance on 1999 Jaguar XK8

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My XK8 recently had two occasions where the "restricted performance" message appeared, accompanied by an amber light and the "check engine" message. When I took to the local dealer, they could find nothing wrong, except a crack in the drive belt and need for a fuel filter. The lights went off, on their own, but have since reappeared. Could it be the drive belt that's causing these messages? The dealer's service technician also indicated that they showed one of two "codes" P11-11 or P100 (as best I recall). Can anyone offer thoughts on this?
(1) Answer
p1000 is a dtc that means the vehicles has not fully cycled through its diagnostics a p1111 means all systems checked out and are operating fine. restricted performance can be a number of things from low fuel pressure, either from a bad pump, clogged filter or injector. Also mass air flow sensors, 02 sensors, plug wires or an ignition coil becoming faulty are usually the top culprits. Check for trouble codes before attempting to fix and breaking the bank!!!!!!!!!!!!