With the codes you are getting it could be the coil pack, spark plug, coil relay or injectors. With the fact that you were getting only one code for #2 and now you are getting it for #2, #3 & #5 I would be first looking at the plugs and relay then the possibility of the injectors need cleaning. At times a can of BG44K added to the fuel is all you need but it is hard to say. And yes a low battery could cause this problem.

Link http://jagrepair.com/images/AutoRepa.../jagxk2000.pdf

 

Thanks for that, and the manual. I have been starting the car and driving often in an effort to replicate the problem and, once again, record the codes. However, the only change is its now changed from P1000 to P1111 which I believe means its completed a "learning cycle" and everything is OK. You may be right about the injectors. I've always suspected a fuel problem as well. I had a new fuel pump put in it about 1500 miles ago. Which, occasionally, make quite a bit of noise, The only consistent variable in all this is when the car has been driven, then sits out in the hot sun. I know that sounds weird, but when it goes into limp mode, its either been sitting in the sun, or I'm on the highway. Never around town. Thanks again

 

Before changing any additional parts, check the battery voltage across the terminals after the ignition has been of for at least ten minutes. There should be a minimum of 12.6 volts across the terminals or the battery should be replaced.

If the battery has proper voltage, next check the fuel pressure at the schraeder valve on the fuel rail. Fuel pressure should be between 3 and 4 bar at idle and 5 bar at WOT.

 

Check the battery and let us know what you come up with.

 

Not running, it reads 12.9. It's a relatively new battery (3 years old) that's on a trickle charger in the winter. You suspect something electrical?

 

Just checked my XKR - it was 12.8V.
I would check fuel pressure next per the advice (attach gauge to schraeder value after unscrewing plastic cap, I believe at rear of right/passenger side fuel rail underneath plastic V8 cover) - certainly low pressure can throw misfire codes. This happened on my XK8 when the fuel pump was failing - showed up initially in hot weather, when pump had been running for some time, initial pressure was good, then started to degrade after a few minutes, ending up in restricted performance and misfire codes. Also gradually lost ability to hold pressure after engine switch off. Of course you have a relatively new pump, but I suppose it could be a dud, or fuel pressure regulator issue, or....anyway I would follow the advice to eliminate low fuel pressure as a possible cause.

 

ELM327 V2.1 HH OBD 2 OBDII Car Auto Bluetooth Diagnostic Interface Scanner Tool

has worked very well for me on my XK8

 

It is hard to say if it is electrical or mechanical or fuel. You need to make several checks to identify what is not taking place. Remember this is not your dads Buick! You are dealing with a computer run car and all it takes is a poor connection, bad relay, equipment failure or just low voltage and nothing works right. The best thing to do is step back clear your head and take one thing at a time.