Would appreciate any thoughts on this issue. Twice within the past 10 days, my 2008 XJR has died while in stop and go traffic. One time was on a busy surface street when the car had been stopped at a traffic light for about 5 minutes. The other was yesterday after the car had gone through about 10 minutes of stop and go on the freeway. In both instances, the amber check engine symbol came on as soon as the car killed. I put the car into park and restarted both times, with no subsequent problem. The check engine light went off and stayed off. Both days were reasonably warm (around 90 degrees) and yesterday was quite humid (can't recall on July 12).

For what it's worth, the amber check engine light also came on and stayed on while the car was stored during the past winter. It first came on (and stayed on) when starting/running the car in Feb. Similar when I restarted in March and took for a short drive and then again in April, finally going off after a couple of days driving it.

My fuel filter was just changed in late April as part of the 60,000 inspection. I use 92 octane fuel religiously. The car has 63,000 miles and is stored from Nov.-Apr due to the Minneapolis winters. I've noticed the RPMs at idle are about 600 which seems a little low to me but the dealer has told me is computer controlled and not out of line. I have an appointment next week but would appreciate any feedback on what might be causing the car to kill in stop and go.

 

Before you go to the dealer, try fully charging your battery.

Prior to doing this, see what the output of the alternator is at the battery terminals.

Once the battery is fully charged, take the same measurement.

 

Thank you. Good idea.

 

You need to ask the dealer to scan for codes.

Tell them them you want to know exactly which codes were found.

92 Octane is too low, I use 95 minimum.

 

+1 on the battery voltage and...
+1 on the codes too: if there are P050B-85, P0131 Or P0151 codes you may want to check out TSB 30313 (ECM update/re-flash).

It is not the octane, I literally have tens of thousands of miles on 4.2 supercharged motors and we can only get 91 max in the far western U.S. (unless I go for racing fuel).

I did get a tank of bad fuel once and that threw up all kinds of warnings including the check engine light and restricted performance, it never stalled though. It cleared itself with the next tank of premium, thankfully, as I happened to be on a 4K mile road trip in Western Wyoming.