2001 xkr. Occasional restricted performance but only in manual mode. It will not do it when left in drive. How hard you drive it makes no difference. I drive the hell out of it in drive and restricted performance does not come on But when keeping it in fourth or just randomly going into manual shift restricted performance will light up. No codes. Turn the car off restart and everything is fine . Have had it in to Mechanic they have no clue. Never seen this before without throwing a code . Could it have something to do with the shifter? Any advice appreciated.

 

When i get this kind of unexplained electrical weirdness the first thing i do is take the battery to a shop that can do a battery load test properly, even if its new or seems ok,

lf the battery is Ok i would then work through all the earth straps in the boot, right side of engine under exhaust manifold and any others you can find.

l would also get a good can of electrical contact cleaner and some gas welding nozzle cleaning files go through every connection block you can open up.

...........................moneys on the battery and or connections

 

Sounds like it could be the J Gate position sensor - assuming the same as the XK8 there is a microswitch that indicates the lever has passed across the bottom of the gate. If this sticks or does not operate the car sees an implausible position for the gearbox vs the J gate and - limp mode. You would need a decent code reader on it to pull TCM codes off after it happens but before you switch off the engine.
You may be able to get it to fault key on engine off by going D to manual and back.
That's the cheap possibility!