Code P0171
 

I have a 2001 XK8 and only when on the beltway does the engine light comes on. My code reader denotes only P0171. My local mechanic suggested replacing the mass air sensor. I cleaned the sensor with the appropriate cleaner and there is no change. The engine light does not come on during normal city driving. I suppose there could be a small vacuum leak or a defective O2 sensor. Any suggestions?

Air leak - bet it’s the accordion section on the plastic air tunnel
 

The Fault only registers when the lean air/fuel mix is 25% out of tolerance, so explains why you only have the problem when your on the freeway,

As a symptom, the Car should be feeling sluggish too when accelerating and MPG drops.

Obvious place to check is the plastic air tunnel accordion section, between the air filter box and throttle body, which often cracks at the bottom aka cooked by the heat. Then you’re hunting all over - PCV breather pipes, cam cover, VVT seals etc. A smoke test can help.

Welcome to the forums Bburka,

When you've found the cause of your P0171, please follow this link New Member Area - Intro a MUST - Jaguar Forums - Jaguar Enthusiasts Forum to find the New Member Area - Intro a MUST forum and post some information about yourself and your vehicle for all members to see. In return you'll get a proper welcome and some useful advice about posting to the forum.

Graham

P0171
 

Don't drive on the beltway ! I spent years commuting on it, and now avoid it like the plague. But seriously, the accordion tube between the air filter box and the throttle body usually gets cracks over time that cause air leaks. Or it could be the MAFS (mass air flow sensor) - they're pretty cheap now. Or could be dirty injectors. You could run some fuel injector cleaner through it. This is a pretty common code, but can sometimes be hard to run down.

Thanks all. Agree that smoke test is in order. I’ll check the accordion section. There is no effect on engine performance.

That you can tell. And, you can’t order the accordion section by itself. You can buy a new intake tube, whether the original plastic one, or an aluminum one. You can also cut and join with silicone hoses (3 inch) or you could also have one fabricated out of any material you want, but the favorite seems to be either titanium or aluminum.

Go with 3.25" Silicon hose if you can find it.... 3" silicon hose is damn near impossible to get on BOTH the 3" diameter breather tube pieces. One end goes on with a little creativity, but the other end turns into a few frustrating hours, much profanity, and VERY sore fingers. Had I purchased a 3.25" hose to start with, would have been a 4-5 minute job to slide the hose on both ends, adjust the positioning, and tighten the clamps.