I'm getting the P0171 (Too Lean at Idle Bank 1) error message, and am slowly working my way through the diagnosis process.

I did a smoke test today and noticed a few small leaks. It does look like there is a small leak around the intake manifold gasket, which I plan to address.

Notably though, there was also a lot of smoke that came out of the spring mechanism for the butterfly valve on the throttle body. Is this normal, is this a common place for leaks? Has anyone tackled this before? Can the X350 throttle body be mechanically rebuild with new bushings and seals?

Thanks,

M

04 XJ8

 

The manifold leak could give the lean code on one side if the leak is on the lean side. The throttle body would more likely make both run lean. Check your fuel trim values to see what is happening.

 

I replaced valve cover gaskets and intake manifold gasket on my 4.2 N/A as well chasing air leak. After the work there was much improvement nevertheless still there was some lean condition on one bank only. Did a smoke test few days ago and found air leak near the butterfly valve spring. Well, as long as it runs nicely I'm not gonna buy an entire throttle body since sealing the rest solved the problem in the majority however maybe there is somebody that managed to seal that leak coming from TB?