I'm getting po171 & po174, lean on both banks. 2002 lincoln 5.4 intech with 99k miles. I've started the simple stuff, cleaned the MAF, checked for vac leaks. The books show a lot of possible causes, how would you decide where to start? What would a service center do first? Thanks for any help.

 

Start in back of the throttle body elbow. Follow the PCV system and check it back there, by the firewall. That's the most common area where the leak and cause lean DTC's.

 

Found it! Right where you said. I had to remove some plastic on the intake to get to it. The backside of the rubber 90 that goes into the intake was rotten.

Thank you so much for your help! I'll replace it & clear the codes and see what happens. I betting it's fixed.

 

Good deal, yea, that's a common problem.