I've been chasing a reoccurring Restricted Performance notice tripped by codes P0172 and P0175 indicating that it's running rich on Banks 1 & 2.

I diagnosed a bad O2 sensor last fall and replaced it which seemed to clear up the issue for 500 miles or so, but it's returned.

I'm suspecting that unmetered air is entering somehow, but don't see how. The air filter is clean and tight, as is the MAF sensor. There are no cracks in the intake snorkel and the throttle body gasket is tight. I checked the MAF connection and tweaked the pins to assure good contact.

Any other ideas?

Thanks!

 

Would running rich be indicative of an air leak ? I thought not ?

Wouldn’t those indicate not enough air, plugged up air filter or a squirrel living in the intake pipe to the air box ?


Or too much gas, as in a leaky injectors ?

 

I've wondered if my injectors might be worn out after 24 years and 150,000 miles...

 

I don’t know much about what causes injectors to wear out. Mine have 189,500 miles on them. No obvious signs of being worn out.

But injectors can be impacted by deposits which can cause lean conditions by narrowing the orifices or a rich condition when they don’t close properly and dribble gasoline.

Z

 

Maybe a dirty MAF needing a clean

 

What are the fuel trims, especially long term? I would replace the MAFS with the proper Denso unit and see if the codes return.

 

A rich condition can caused by the computer thinking it has more air, if you will, then it truly has. The computer enrichens the mixture to compensate. The O2 sensors try to lean out the mixture, to no avail, and then they inform the computer, and you get a SES light. In layman's term. This condition is often caused by a flaky MAF reporting higher airflow than what's really available. It could also be restrictions in airflow, but you'd need a really, really dirty filter. Also, if you haven't tried it, get a can of MAF cleaner and clean the filament well before spending stupid sums on an OEM MAF.

Another thing that can cause rich conditions are fuel system malfunctions, like a leaky or stuck-open injector. These are often easy to spot by pulling the plugs and examining them. If one, or more, are dark and sooty, odds are you have an injector issue. If they're all sooty, refer back to the MAF.

Anyway, that's my 2 cents from experience with other cars. Knock wood my Jag doesn't have this problem. It's had almost every other problem, but not this one.

 

skewed maf

 

My 2000 XK8 had that when I bought it. Turned out to be from high fuel pressure (about 90psi) due to a blockage of the fuel return line at the tank. Fuel pressure regulator couldn't do its job.
Check your fuel pressure.