From what I have delt with, the DPFE will cause a lean mixture on both banks. What it does is corrode inside. As a result, it doesn't sense properly and causes the EGR to stay open longer than it should. Thus, you get a lean mixture. As far as a vacuum leak at the brake booster, yes, it will cause a lean mixture on both banks.
I'm glad the dealer didn't take you. I would have done a wet compression test if it was a valve or the rings. Rings would have cost you a hundred bucks if you did it. As far as a valve, remove the head and reseat the valves. I just hate when dealers tell customers they need a new engine when it can be a cheap, easy fix. Sorry if I sounded upset.
Let me know if you have other questions. My guess is the DPFE is setting the code. Keep in mind, if you had a cylender that wasn't firing, the O2 sensors should have thought it was running rich because there would have been unburned fuel.
I'm here if you need anything. Let me know and I'll do my best to help.
Monday, October 4th, 2010 AT 9:08 PM