newyankee wrote:It's none of that. They all do that, believe it or not (read posts on jag-lovers by steve)
You are talking about lean misfire at idle, or at low revs with no load. To an extent
they 'all do that', as Jaguar built lean burn into idle and low rpm off throttle to save fuel and provide quicker cat light up on ROW versions of the V12, but it shouldn't affect drivability under load and if it does there is something wrong. You didn't provide a link to 'Steve's' posts, but I'm guessing he eventually did some research and worked that out did he?
Both our '94 XJ12 and our Marelli ignition XJS have the barely perceptible lean misfire at idle and low revs off throttle, but it doesn't affect the drivability of either car and it is always there when hot, it doesn't go away then come back after you stop for 15 minutes. There is no vibration at idle on either of our cars - we can do the old party-trick of standing a coin on the engine at idle with no problems whatsoever. There should only be a barely audible (not felt) occasional 'pop' in the exhaust from lean misfire.
I take it in all the things you replaced, you did check that the outer half of the crankshaft damper with the timing star hadn't slipped relative to the centre hub? This is a very common fault on the V12s that throws the timing out. If you did you obviously did this with a degree wheel and dial indicator on number one piston to be 100% sure it hadn't slipped, as the V12s are very sensitive to this because of their very high compression ratio. It's amazing how many people miss that particular fault.
Oliver's car has been off the road for many years. Has had fuel pump issues, a broken petrol tank cap (so who knows how old the fuel was in the tank), water through the fuel system, voltage issues, and as yet we don't know what the state of the other components are on the ignition system. There have been a number of other posts about these issues too. As per Chris's comment, there are many other issues to potentially work through on Oliver's car. So in fact it could well be 'all of that', and more besides.