My 2009 XJ has just started to misfire when warming up and in the first few miles of driving, after ten miles it seems to go away, the dealer said they found a misfire code but couldn't find anything wrong, it went away and they put it down to bad fuel...It has never really misfired before now, now though its every day. could it really be just bad fuel or something bigger?
any insight would be great before I take it back in and get it looked at again.

2009 XJ 82,000 miles California car.

 

I suggest that you find a good independent mechanic and don't use dealers.

Have it scanned and post any codes here.

 

Bad fuel? Really? In the first place, the Jaguar dealer mechanics are one of the worst ones out there as I wouldn't trust those monkeys for a simple oil change. I mean, they couldn't find anything because they simply didn't know what to look for. Did they at least indicate on your bill which cylinder was misfiring? If they did, I would simply replace the coil pack for that particular cylinder, and you would have in all likelihood fixed the problem.

 

Thank you, I have a scanner on the way, I will post the codes

cheers!

 

Note taken! they did not mention any codes regarding the miss fire, I am going to scan the car myself and see what codes I get, then go from there, Thanks for the advice!

cheers

 

A failing ignition coil can cause misfire(s) without a pending DTC or turning on the MIL.

 

Hey Chris,
I had a similar problem - slight misfire upon cold start up. No codes, though I found that the fuel trims were a bit out of wack.
Anyhow, problem turned out to be slight vacuum leaks at several places:
- Throttle body port for brake booster line (its a brass and plastic fitting; just press in plastic sleeve to tighten. This was the biggest leak)
- PCV valve O Rings (which seal valve to RH valve cover; replace rings or - as I did - complete valve - second biggest leak)
- Oil dipstick O Ring (seals to dipstick tube)
- Evap valve vacuum tube O Ring at throttle body (valve on top of LH valve cover)
Don B of this forum pointed me in the right direction. Suggest you buy an O Ring assortment (any auto parts place) and replace the likely culprits - only takes a few miutes

Hope this helps!

 

So.... I got my misfire codes: P0307 cylinder #7 and P0316 misfire on startup, I replaced the 4 coils on the #7 side and all 8 spark plugs...runs great now,

Thanks to all who weighed in...

cheers!