My 2009 SC XF idle goes up and down and has got so bad it dies when I come to stop lights. Have had in and out of shop for past 4 months. No one can seem to fix the problem. I no longer have power when I step on the gas pedal. It comes up restricted performance. Showing miss fire on 3 cylinders even after I changed all the spark plugs. I saw a thread or two noting similar issues, but no advise how to fix. Does anyone know what the issue might be?

 

Is "misfire cylinder 3" the only code you have? If so, I would recommend pulling that coil out (Should be second one back on the passenger side looking at the front of the engine) and checking for oil in the plug hole. If there is no oil and you have access to a scanner, swap that coil to another cylinder and drive it again. If the misfire moves, to say, cylinder 4 then you have a bad coil. If it does not, then I would check that the injector is firing (with a noid light. Don't forget to check the spark plug for being wet with petrol. It could be an injector is hung closed or hung open). If the injectors check out, I would move onto checking compression on that cylinder (wet and dry).
Hope that helps some.

Cheers

P.S. I have also seen numerous air leak issues on these engines. Especially when starting cold. If you have any lean codes (e.g. p0171, 0174), I would target those as primary.

 

I'd bet it's related to dirty injectors. You could run some BG44K ($20/can) through the gas. One can per full gas tank. Otherwise you could pull the injectors and have them cleaned. I run a can of BG44K every few months. Previous to that I had issue with dirty injectors causing restricted performance. The dealer cleaned the injectors under warranty and told me to run a can of BG44K through it every once in a while. I haven't had an issue since so I've stuck with it.

 

Not to be all over the board as both of the priv suggestions are good places to start, but given the year of your XF, and what you've already done I would start with the O2 sensors, if you can get a live scan and it shows slow or no transient response that will cause the symptoms you mentioned, and a bad O2 sensor does not always throw a "check engine" light.

 

Could also be bad ignition coils. Not sure how reliable the Jaguar ones are, but the symptoms are classic bad coils.