look at all those zero's, now your not giving kids asthma at the lollipop stop!

I'd clean up the throttlebody, partload breather orifice and MAF, there's a great pdf by a member that carries out all 3, takes about an hour. You'll find it here...
DiY_Document_Clean_MAFS.pdf

If you do a 'hard reset' as well after doing these little maintainance jobs, you should see even better response and gas mileage.

(btw, got asthma myself)

What are the before and after fuel economy numbers?

Prior to changing the sensor I couldn't get better than 16 MPG. Now consistently getting 21mpg over a tank

Hello,

I'm new to this forum, but I have been fairly active in Finland's own jaguar forum. However, there are not too many x308 XJRs in Finland, and therefore I figured it would be best to place my question here.

So I ran my '98 XJR to MOT couple days back, and it actually passed without fault. However, there was a slight issue with the emissions which rised my concerns: the emissions were okay when measured from the right tail pipe, but on idle the emissions from the left pipe were way off (considering HC and CO I think). Since there is the middle silencer which intermingles the exhausts from left and right banks I could only assume that the fault is after this silencer. Seems kinda odd to me since there are only two silencers after that and I think they have nothing to do with the emissions, and they even looked alright?

Sorry, ment CO2 and HC.

It could be a number of things, maybe a collapsed silencer in the centre box, might also be an unmetered air leak or faulty O2 sensor. Are there any warning lights and you able to plug in an OBD code reader?

No warning lights what so ever. Yes I should see if any codes has come up in the past few months it hasn't been plugged in. I just wondered that shouldn't the emissions be bad from the other exhaust end as well like in the case of OP's car if the cause would be before the centre box?

Maybe I asked the wrong question. I know that there can be many reasons to bad emissions and no one can say what the cause is just by knowing that the CO2 and HC readings are off the limit. What I meant was how is it possible that the emissions on idle were okay measured from the right tail pipe but not okay from the left one considering that the exhaust gases get mixed in the center box?

I don't believe the two exhaust streams get completely mixed in the center silencer (picture of cut-open silencer here: https://www.jaguarforums.com/forum/x...ut-out-167869/)

Thanks, that's what I figured as well. So back to square one and looking for faults with the left bank! Although it's running and starting up well, there probably has been an ever so slight misfire every now and then in neutral/park when idling, and the fuel consumption I think is slightly higher than what it was during last summer, but that might also be due to colder weather (lots of cold starts). Also when revved in neutral sometimes it pops a bit while the revs come back down. Maybe a leaky injector? Well gotta start with the codes I guess.

I don't think you mean CO2. It's meant to create that.

I think you mean CO.

Not just the codes. Check fuel trims too.