Hi all,

I’m trying to chase down a random misfire at idle - not even enough to log a fault I just occasionally feel it. It’s recently been converted to gas (did this beforehand) so I can rule out the file system as it does it on both.
Put new plugs in and after fixing various vacuum leaks trims aren’t to far off where they should be...

So I’m now pondering what my issue could be?

In drive with brake on the foot it hardly misfires at all and when driving it doesn’t do it ever...

So all I can think that’s left is coils but seems odd they all do it however they are all 11
Years old but just wondered if what I describe sounds like dying cool symptoms?

Thanks Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

G'day,
Happy New Year. I had the same problem with mine, 2004, L322 just purchased and a long drive home some 1500km. Car drove fine until arrived home and started missing on #8. I replaced all spark plugs and still missing, mine was showing the fault. I removed the #8 coil and moved it to another cylinder, problem moved to new cylinder.
I purchased 8 new coils when they arrived I threw out the bad one, fitted all new ones and keep the rest as spares.
Cheers

Unnecessary quote removed

Dan I have a 4.2 on 185k miles had it from 60k and mine has always done it never been able to find a fault and it is only on idle and totally random one of the Jaguar engineers who serviced it years ago said it was not uncommon and was almost like a signature of the engine I have however never replaced the coils . I put it down to fuel pressure on idle varying anyway I have done 120k miles with it with no problem

Thanks RSW - I had that engine before and it was a lot easier to track down as you say. Moving on mine made no difference,


Sandyt - are your fuel trims slightly lean at idle do you know as whilst mine are mainly sorted and not enough to put a light on now at idle they sit at about +10 both banks even though I’m air leak free after various smoke to eat and fixing things... Current stable:
2006 BMW M6
2007 4.2 V8 S/C FF
Gone:
2002 4.4 V8 FF

Not sure Dan will have a look later if I get the chance have to say apart from the od almost like a hiccup runs like a dream

It could also be the leads they are in a harsh environment and may as they get older get too hot but then you would expect this to show up on higher revs as a fault