New to the board, and sorry for the long post..
Came across this site looking for some info on a problem (with many answers I think).... here's my story...
99 XJ8 with 74K miles. Has been a beaut and have had no issues...until now.
I have the "Check Engine" light and the "Performance Restricted" message. Took to local dealer and they replaced a cracked vacume hose (probably the breather hose). Gave it back to me and within 5 miles, "Check Engine" light again. Took it back to dealer and they had it for 4 working days. Told me they missed another cracked hose and all should be well...well, after about 30 miles "Check Engine" light again, "Performance Restricted" message (but it went off shortly, Eng light stayed on).
Here is what my limited knowledge is telling me. I think when they replaced the 1st hose, they should have reset the Air Fuel Ratio back to standard. If it was a vacume hose, then I'm guessing the AFR went too rich to adjustfor the added air intake. Could be the same issue on the 2nd hose. Anyone know if there is any validity to my "guess".
The only other thing I can think of is an O2 sensor might have gone bad, but I would think the dealer would have seen that on their scannalizer, no(??)
I did fill up the gas tank pretty full....OK, I overfilled it... and maybe it's as simple as that. If that is the case, how best to clear the code so the darned light goes off?

 

Very good question, and thanks for the reply. Dealer tech didn't provide the codes, just told me they fix the problems and it test rode well. Will the dealer provide the fault codes if I ask them?... On previous cars I've had, they were two button on the radio I could push and hold and the fault codes would show. Do Jags do the same?

 

Talked with mech today, didn't give me code specifics other than to say it was throwing "Bank1 and Bank2 codes"(???)...
Service writer wanted me to authorize them checking/repairing the timing belts and/or tensinors (@ $2400). I discussed with the mech that if was a timing issue the car would let me know by coughing, spitting and/or generally running poorly. He actually agreed and I got the sense he was trying to tell me that it could be "the sensor"... which sensor he didn't elaborate on but I don't think he was talking about the O2 sensors. I agreed (@ $540 or so) to replace this "sensor". Is my assumption anywhere near correct about the car running poorly if a timing belt/chain(s) and/or tensionors were out of whack?? BTW, my "initial" fault codes on my invoice show P0171 & P0174. They replaced two hoses (vacum and "another one") but didn't solve the issue.Any feedback is appreciated.

 

Been catching up on my reading (this forum) and it seems a common issue with the 99 XJ8 (chains and tensionrs). Anyho, I had them replace the sensor, and light has stayed off for 50 miles (better than before). Time will tell if I wasted $438, but rather that than $2400. This is what how the invoice reads:
" 1 LNE1620CB Sensor - Air Flow - $389
Verified concern-codes P0171, P0174-check fuel trim at idle-trim at 0% and on hwy is 19.7-called tech line-tested brake booster, air injection valve, and engine vacum-OK-replaced mass air flow sensor and test drive-Engine light is not on- fuel trim is at +11% at idle and +14.2 at hwy speeds-contact tech line againnext step is to check timingcustomer to monitor".

Can anyone deciper if long term problem is solved? Don't know what the +11% and +14.2% means, unless it's the AFR settings...???... Is good?? Is Not So Good?? Is Bad???