I have an '04 XJR. Last summer I had a few instances of the dreaded Restricted Performance error, with the accompanying Christmas tree of warning lights, DSC/Cruise not available, etc. Each time the car wouldn't rev over about 1200 rpm, and full throttle would move the car maybe 5mph - enough to get it off the road and that's all. Each time turning it off for a minute and restarting cleared the fault, but with the CEL on and a code for the TPS. I cleaned and waterproofed the connector and haven't had any further problems.

Yesterday morning was the first really cold one here, about 20 degrees. I started the car and it cranked normally but the seat didn't move forward, which has happened a few times in the past. I turned it off, removed the key, opened and closed the door, restarted, and the seat moved to the driving position, However, it now gave me a Restricted Performance message, but no CEL and no other lights. The car would rev up, but sluggishly. I restarted it a few times but the message remained. I drove the car about six miles to the gas station (it had about 1/8 of a tank) and it drove at normal speed. It just felt like it had half the horsepower, kind of like when I drive my brother's NA XJ8. The car had warmed up by the time I got to the station, and after I restarted it the message was gone and the car was fine again. No CEL, nothing with my OBDII reader (Torque) and nothing with the WDS.

I couldn't find any posts with those symptoms. Anyone ever experienced this?

 

Sounds like a failing battery. Happens all the time on S-Types & XFs. They start the car but volts and power are low and weird things happen.

 

A battery problem didn't occur to me, but I know a bad battery can cause all kinds of things. The first thing I did when I bought the car a little less than three years ago was replace the battery, but I'll get it checked.