P0171 Code
 

I put my XK8 in storage last November without solving my "lean bank one" trouble code. My mechanic performed a smoke test last week and found cracks in the air intake tube between the filter box and the throttle body. He also cleaned the MAFS. The code came back after about 100 miles today. We have not analyzed the fuel flow, but I used a few tanks of injector cleaner last fall. Does anyone have any suggestions where to go next without eating up a ton of tech time?

The 0171 is a lean condition. I would take a look at the part load breather tube that runs from the left side of the engine.

The best would be to start with some data, especially the fuel trims. I suggest you look into acquiring an ELM327 OBDII port device to pair up with a smart phone (and TorquePro for Android). The device is a few dollars only (check eBay), same for the app.

Once you have the trims, you can better better see what the problem could be. If trims are high at idle, it is more then likely an air leak of some sort. If it is more inconclusive, you might want to trow in an air flow meter (these can be had for cheap these days, that particular design is very common, fortunately). Another area that has (surprisingly) been known to cause these codes is the VVT seals on the cam cover. Cheap and easy to replace, especially if you see a (minor) oil leak. These harden and become useless over time. Also, the EGR pipe has been known to develop cracks and cause bank 1 lean codes. That pipe is below the throttle body, right by the firewall on the passenger side. The bellows can crack over time allowing un-metered air in.

Best of luck, keep us posted.

My wife's 2006 XK8 threw a P0171 code back in mid-February. After trying a new mass air flow sensor and fresh spark plugs to no avail, a smoke test at my trusted indie shop revealed air leaks at the two VVT O-ring seals as mentioned in the post above. Two new VVT O-ring seals resolved the issue. The failing VVT O-ring seals were only two years old but they had already become hard and brittle. I had purchased cheap ones online and will not do that again. This may be one of those cases where the OEM part is indeed better than the various aftermarket parts....

I do have a very slight oil leak at the valve timing solenoid on bank 1 and it started last summer when I began getting trouble codes. I'll have to ask my mechanic if the smoke test showed any smoke coming out there. Does the valve cover have to be removed to take out the solenoid? My MAFS glass bulb is a brownish/red color and it does not appear any different after spraying it with cleaner.

If you're going to remove the actual VVT solenoid, then yes the cover has to be removed. If you're just changing the VVT seal, then no.




With your model, there could be numerous areas where a vacuum leak could occure. The air intake pipe, the accordion section, at the bottom is known to crack and cause leaks, which sounds like you sorted this already. The rubber boot at the throttle body has been an issue, but not a common one. You also have the part load breather hose that runs from the Bank 2 cam cover, under the intake, to the throttle body elbow, these are a known issue. You also have the small vacuum hoses at the rear of the engine, such as the one for the fuel pressure regulator, and cruise control.


You can try taking some brake clean, start the engine and spray the intake area down, throttle body, air intake, etc to see if there is a change in idle speed.


I have also seen on many occasions the MAF sensor be at fault, you can try cleaning it, but the little bulb you're speaking of is not what you need to look at. There is a little window when you look down the bit where the bulb is, there is a wire in there that looks like it has a resistor in the middle of it. That's the one you need to make sure is cleaned. Its supposed to get very hot every few start ups to clean itself, but sometimes its not enough over time. If you clean this, I'd recommend getting some contact cleaner, clean it, and let it dry for a few minutes then reinstall. Then re-check. If the code comes back, then you may need to invest in a hand held scanner as mentioned above that can read various sensors such as MAF and fuel trim data to see what the ECM is doing to correct the issue, if any.

Just an FYI, I've read that it is best to clean the MAF after it has cooled down.

FWIW, I found the 2 seals (original Jaguar AJ82856) on eBay for $20. If you are unsure of the origin of the seals on your car, at that price, you can just replace them. If you see oil, you have to assume air can get in. Just unplug the VVT solenoid connector, use a (dull) tool to pry the seal off, clean out the recess of any oil, and put the new seal in. Maybe 10min per side, no wrench involved, the VVT actuator remains in place.

You might have to double check for your car, but upon confirmation of the part# from forum member Jon89, I found a Denso 197-6030 (in this case, a NEW Toyota part) on eBay for $23. As you already know, this part is just as easy to reach and replace (just pay attention to the o-ring).

Best of luck, keep us posted.

VVT seal
 

The new seal for my VVT sensor has resolved the lean fuel mixture issue. Thanks to all the forum members who offered advice on fixing the problem.

Good news!