I have a 2001 Vanden Plas that threw a check engine light with misfire codes - P0300, 0301, 0302, 0303, 0304, 0305, 0306, 0307, 0308, P1316, P1111. All related to misfire. Could be related to a host of things but where should I start? Coils?

 

would be unlikely to have 8 bad coils. More likely you a wonky sensor like the MAF, cam sensor, VVT, or similar that may be causing the issue. Could also be a wiring connection to the ECM, a bad ground, etc. You will likely need to spend some time determining when the misfires occur. Not sure, but even something like a bad or blocked EGR can cause misfires.

 

A failing or weak battery can cause random DTCs. Start any diagnosis with a fully charged battery that has at least 12.6 volts available across the terminals with the ignition off when checked with a voltmeter.

 

When it is all cylinders misfiring - P0301 - 0308 - it is almost always a bad secondary tensioner causing faulty timing. Have they been changed?

Once, over on the XK8 forum, everyone jumped on timing -- moi, aussi -- it was a bad lead to the coils. Only time on this forum, that I remember, where it was NOT timing!!