My 04' XJ8 VDP had been throwing the P0171 & P0174 indicating both left and right banks lean. Normally you would think vacuum leak. Checked all over for vacuum leaks which seemed obvious. Even broke a brittle plastic vacuum hose to the PCV valve and replaced it with rubber. That PCV valve generates a lot of vacuum leak noise but is not leaking. Still the codes came back. Even though the was no indication or code for MAF Sensor, I thought maybe its not reading the air correctly and causing the engine to run lean. Cleaned it and codes returned.

Drove over to AutoZone and purchased a replacement/rebuilt MAF Sensor. Two screws and a plug to install in a minute. It fixed everything and the car ran better than it ever had. The throttle is so responsive it's feel like its supercharged. It would appear that the MAF Sensor degrades without throwing a MAF Sensor code causing other systems to compensate for bad info causing codes in my case. For $79.00 you may be surprised at the improvement in performance of your car.
Cardone Reman/Mass Air Flow Sensor 74-50009 at AutoZone.com
Give it a try Best performance improvement I have ever seen.

My Pirelli P Zero Nero tires worn out after 22K miles. Never had very good ride quality and were especially poor in Wisconsin snow. I just bought a set of Continental Pure Contact P235/50R18 97V rated tires. Snow storm was coming and needed tires. At $188/installed@ plus tax. So far extremely impressed improved ride quality on dry and snow in 1"-2". Would highly recommend these. I should get three times the mileage also but I would recommend rotations every 5K miles.

Continental USA Car / Light Truck / SUV -PureContact?

Ed

 

Just put a set of Continental Pure Contacts on our Cadillac DTS. I find that they are nice riding tires and have performed well in our first snow of the season. Will certainly consider for the Jag when the time comes. Have not checked to see if they are available in 20 inch.

RyeJag

 

You can often get the same performance boost from a can of CDC Mass Airflow Sensor Cleaner. I clean mine every oil change; its a electronic cleaner with no residue, that claims a minor HP boots on the label (3-7 hp or some such nonsense) It's not really nonsense, as a dirty MAF sensor can inhibit performance but throwing HP numbers around seems kind of silly. Anyway, just thought I would add my 2 cents.

 

Good information on the tires and the MAF sensor. Thanks.

 

Actually I tried the CDC MAF cleaner first and it had no effect. When I changed the sensor out with everything else being the same, that's what made the remarkable improvement. Obviously the issue with the sensor was not dirt, but cleaning as a first step would be a good suggestion.

 

I have used CDC MAP sensor cleaner as well, not sure if it really has an effect or not since the MAP sensor did not appear dirty. I do have periodic P0171 and P0174 errors, that appear to take place after checking the air filter, I assume from repositioning the air tubing and lines downstream from the air cleaner and MAP sensor. I have replace some of the o rings on the breather tubes thinking they may have been damaged or getting less flexible. So far so good at 81K miles
RyeJag

 

I went throught almost the same thing. I went vacuum leak first but everything didn't prevent reoccurring codes. I feel the MAF degrades without failing and the performance reduces so slowly its not obvious. Give it a try for about $70 and 5 minutes, my result was like I bolted a supercharger on!

 

2004 jaguar Vanden Plas XJ 4.2
Hi everyone. A year ago, the engine light came on and I got the code P0171. I cleaned the Mass Air Flow sensor and it fixed it. Now a year later, the engine light came on again and I got the same code P0171 bank 1 too lean. Even though there is a code, there is no warning or engine fault message displayed in the message display inside the car. This time, cleaning the sensor did not do the trick and I now get P0171 plus P1000 and none is reset by disconnecting the battery terminals. According to this tread, MAF sensor may be the problem but before I jump and replace it I would like to know if the symptoms shown by my car points to something else or not.
At start (idel), the engine is a bit shaky and I also hear a tic, tic, tic, tic…… sound. As Engine warms up the shaking stops and the sound goes down but not completely. I have inspected the visible vacuum lines, removed and inspected the intake hoses and they seem ok, and as far as I can tell, there is no hissing sound heard either. I wonder if there is a cylinder misfire situation but I like some help in isolating the problem before messing with the car. Comments are appreciated. If additional info is needed please let me know.

 

See the above post.