The codes kicked in when leaving a rest stop. I have a scanner so I read the codes and P0171 and P0174 came up. The message Restricted Performance also popped up. I just had my throttle body replaced two days before my road trip so I am hoping it is related to that. Tomorrow is the ride home so I hope I make it.

 

System too lean, both banks. You could try cleaning your MAF, it might help, or check to see if there's a vacuum leak, esp around the throttle body since that was just replaced recently.

 

Hi Steve,

P0171 and P0174 are very common codes for lean running, and since you have the codes for both banks of the engine, the most common cause is a leak in the air intake plumbing somewhere between the Mass Air Flow Sensor (MAFS) and the Throttle Body (TB). Since you just had a new TB installed, the first thing I would check is the large plastic intake pipe to ensure that its ends are fully fitted to the MAFS and TB and that the hose clamps are tightened but not so much that the plastic is deformed. Also check the breather hose that connects to the pipe.

If that all looks good, then check for cracks in the pipe. You don't mention the year and model of your car, so I don't know if the intake pipe includes any Helmholtz resonators, but if so, check around the joints where the resonators meet the main pipe.

Other possibilities include a leaking TB gasket, a cracked vacuum line or other vacuum leak, etc.

Cheers,

Don

 

It's a 2003 XJR. I'll check and see if I can find a leak.

 

I got a new MAF sensor and so far so good. I'm hoping if the codes don't come by 250 miles with the new sensor it means it's fixed.

 

Good Luck!