2000 Jag XJ8 Vanden plas...pulling codes P0170 and P0171. this last time..was cruising at around 70mph, cruise control on, A/C off, at about 2500 RPMs or so and it went into restricted performance mode...was there for about 1 - 2 minutes...then went away, 10 minutes later it came back on for 30 seconds...then went away and hasnt come back since...but check engine light is on...

P0171 means "System too Lean" what does that mean?

can anybody help me diagnose the problem?

 

Best advice to a new owner is to go to ebay and obtain a copy of the JTIS CD.
That gives you a basic introduction to systems on your car, and specific diagnostic and repair procedures.

 

OBD II codes do not always identify an exact source of a fault. Your situation is a good example. The problems you describe could easily be attributed to a dirty or inaccurately operating Mass Air Flow Sensor.

 

However, there are other components that could be causing a lean condition. Without a basic working knowledge of your car, you won't understand references to "part load breather tube", etc.

 

So your list of questions will grow, not shrink. That gets a little tedious for all concerned. There is no paper shop manual you can buy to rely on, get the CD and spend a few days with it. If you can't find your answers, you will be better prepared to understand the ones you get here. That's all meant as friendly advice, nothing more.

 

JTO, thanks for the advice. i have a friend who is a mechanic that has exp working on jags. he's going to take a look. in the meantime i will order the JTIS CD on ebay.

 

if there is no vacuum hissing sounds then it may need a MAF sensor

 

vacuum hissing sounds...i dont know what they are supposed to sound like.

here's the latest. i pulled off the intake hose, replaced the air filter and checked the MAF. i assume the MAF is the sensor right above the intake box, the computer heats it up and then measures how fast it takes to cool it and regulates the intake that way. when i took it out it was clean, no dirt or debris was visible. i put it all back together and now i am getting the restricted performance message every time i run the car. the only thing other than changing the air filter that i've done is i've been driving it a little easier lately (i usually have a heavy foot). this morning i drove it like i did before with the heavy foot and the restricted performance light did not come on.

how does one know if the MAF needs to be replaced?

any other advice would be great...i appreciate the help.
i did order the JTIS CD and will do some research myself.

 

That CD will come in very handy, I promise you...not just for this type of resource. Good investment.

What did your jag mechanic friend suggest? Did he look at it, or simply suggest you replace the air filter? It is really easy to break off plastic pieces under that hood with heat and age, so be careful when taking apart harnesses, clips or other parts. If the simple stuff doesn't help your condition, then I would suggest sucking it up and taking it to your dealer, especially if your friend mechanic isn't really familiar with the intake system of the jag and it's electrical components. good luck...and update the thread no matter which way you go surreptitious.

 

he's been very busy and i havent had a chance to drop the car off with him. i did stop by for a few minutes and he showed me where the MAFS was located...in doing so he noticed the air filter was dirty as hell and suggested to replace that while i was at it...

i'll update the thread when i get more information. thanks for the advice. i might just suck it up and take it to a dealer...

 

I'd look for tubes that you think move air around on the top of the engine bay. I had the same problems with my car (although it's a x-type and probably has little if any engine similarities) and it ended up being a rotted tube on the top of the engine. Check for old crappy tubes and see if that helps...