Clock moves forward a half hour completely on its own. I will put it back to correct time then next day without fail it always says it's a half hour past whatever time it is.

Secondly, says restricted performance every now and then, with the engine light every now and then. Car idles terribly rough when this happens.

2000 XJ8

 

First thing I would check, is the battery, and perform a reset just in case (unless recently done already). The restricted performance could be anything, but I would try to get a code reader or have someone try to pull codes to give a better indicator of where to start tracing that.

(I had that happen a couple times over the past year, but after doing a hard reset tracing out another issue, it's not happened since, so who knows, might get lucky)

 

I had recently had to restart the battery because the drivers window would not work as well as the radio display on the dash so what you're saying is I should just try to get it reset again using the negative and positive etc.? Also as far as code rating goes I tried to get them to read the codes when I got my oriole changed about two weeks ago but the light and the restricted performance only comes on every so often and it isn't on for a long when it is on but it does happen frequently . Like I could be driving and it would come on and then 15 minutes later it would go off or sometimes it's a little bit longer of a period of time but most of the time it's every time I crank the car I don't know what to expect anymore

 

Stop at one of the auto supply stores and ask them to read the codes before you do a hard reset. The ECU will store repreated codes, but not temporary ones.

If you know someone with a reader that can access real time data ask to have the fuel trims STFT and LTFT read and report them here.

As to the clock, I'm amazed they work at all, and don't have a clue as to your problem.

 

...and check the age, health and model of battery. These cars are terribly sensitive to a strong battery, and of course the correct model battery.

So many issues have been cleared up by replacing a weak battery, or discovering a previous owner had installed an incorrect model battery that couldn't support the extensive electronic systems in these cars.

.