Timing chain issues unlikely on an 03, it has the updated parts.

 

Well I may be overcomplicating the issue. The car starts obediently and idles ok. Attempting to drive it down the street and being overtaken by bicycles speaks volumes of the performance or lack thereof.
Autozone want $150 deposit on fuel pressure kit so i will go to Harbor Freight tomorrow and buy one ($20). I pulled up a photo of a fuel pump and it does have the sock on the foot so perhaps its not letting enough gas through if gunged up but i expect the fuel pressure reading will reflect that. It does seem to be something that has manifested itself since I bought car so during the 12 miles or so I have driven it including a trip to the gas station

 

What does "working on battery" mean? Did you ever replace it?

 

The fuel filter is located in front of the right rear wheel and it would be a good idea to replace that also. There are several aftermarket filters that fit, so don't pay the OEM price.

 

fuel presuure 52 psi at idle. Battery replaced

 

I'm slipping - fuel filter is in front of the LEFT rear wheel. Sorry.

 

Check your grounds. Specifically the cables that attach to the wall of the trunk and the strap that connects to the transmission under the car.

 

Great help thanks. Will be out of loop in Cuba until Friday so will try latest checks on return. I do feel confident we can root out this problem just by process of elimination. Please keep your tips coming in my experience this is something I've missed although now that fuel pressure is high I am wondering if there is another fuel related problem as car starts and revs healthily then begins to droop as it remains running.

 

Did you check the fuel pressure when the engine was losing power? It could still be the filter.

 

Yes back in town and fuel filter sounds obvious but good way forward. I didn't know it had one. Thanks

 

For the 4.2 XK8, you can find cheap ($25?) air flow meters. Look for a Denso 197-6030. Disregard the brand, these air flow meters are very popular with many car makes. Nothing good comes from a bad AFM. Also check for all possible air leaks around the intake tube (top and bottom), heads and throttle body. Every oily spot is likely an air leak, too.