The other day when I started my 2002 XK8 on a cold morning I got the "check engine" light, again. I had been dealing with this issue since I got the car in December of 2012. I have replaced one O2 sensor and both knock detectors, and it went away long enough for me to pass smog test here in California. I scanned the ECU with my Autoenginuity software, and it showed no codes for the light. This was a couple days after the event. But what I did note is that the LTFT is running at 18.5% for the bank#1 and 19.5% for bank#2. I have read ,and I think, understand how fuel trims work, largely because of an excellent primer put forth by XJRGUY.
I looked for any source of air leakage after the mass air flow. I used starting fluid to spray in different areas as I watched the readouts on the laptop. I got nothing. I retaped the pvc tube that looked a little suspect, but no change. So I finally just told the scanner to clear the light and went back to driving it. It seems to run OK. My thinking is that because my trims are probably close to the limits that it tripped a code when it was cold because the ECU could not provide enough extra fuel to compensate for the extra air. Does this sound right? Do you have any ideas of where else to look? Could it be something besides a vacumn leak?

 

H2O has a recent thread for a similar problem and it turned out to be sealing in the intake manifold that was the culprit.

https://www.jaguarforums.com/forum/x...ir-leak-87618/

Since it's both banks with similarly high values it would tend to suggest something common to both sides.

If you've given the intake tube a good going over you might check around the seals where the tube meets the throttle body and the gaskets in the intake elbow. On the back side near the firewall there are fittings for the brake booster vacuum, EGR and other small connections. A leak anywhere along one of these take off vacuum tubes could cause your problem.

You could also check and carefully clean the MAF itself.

Sounds like you're on the right track. Good hunting.

 

It could well be the MAF.
I looked at your earlier thread (July - how time flies) and couldn't see if you'd cleaned or changed the MAF.
As you know from your homework LTFT's that high are either air getting in after the MAF or the MAF lying about airflow or temp.
As Charlie says an inlet manifold leak on both banks would be odd.

 

I too had a similar issue, when checking for for air leaks watch the stft... as it will respond right away. My ltft was at +18... stft was +23. As I srayed the brake clean under the rear of the intake manifold, the readings plumeted! When I removed the intake manifold, I discoverd the seal to the intake elbow was leaking ( as the other guy suggested) I think this was my fault from cleaning the throttle body using harsh chemicals that attacked the seal. Anyway, now that it's been repaired, the stft has retuned to -1 ~+1 and the ltft is comming down all the time and the cel has been off for over a year now. Is yours a 4.O or a 4.2 ? I have an '03 4.2 but I think the intake elbows are the same. BTW... I also found about 25 hp when doing this repair! but thats for another thread.