07 Q7 4.2 008585, 008583 and 005241 lean at idle codes and brake boost mech failure

[jschick]

I just bought this Q7 4.2 and drove it over 100 miles to get it home, the only code it had when I test drove it was the brake booster mech failure, no other codes on test drive or on the way home. But now 200 miles later it throws all three of these codes after about 5 miles of reseting.... lean on both banks at idle and brake booster failure. brakes are maybe a little stiff but not bad, idle is good and smooth, cant find any vac leaks. thier is some suction when I remove the oil cap but not much, but idle does change slightly.
I don't see many of the 4.2's in my area and no Q7's so not real familiar with them. I plan on ordering the PCV valve but it will take a few days to get one, any thing else I should be looking at?
the A/c condensor drain was plugged and it was dripping water on the carpet on the ride home so I did clean it out when I got the truck home ,but I don't see any vac lines around their I could have knocked loose?? that is all that has changed from the time of the test drive to the next morning. (basically I just used a yard stick to wiggle the drain nipple to get it to drain)

[87supraman]

I wouldn't think your PCV is bad. I would be looking at that brake booster. Try pumping the brakes with the engine off, when the pedal gets stiff hold it there and start the engine. If the pedal goes in a bit the booster is most likely operating. Are you scanning with a Ross-Tech cable?
http://wiki.ross-tech.com/wiki/index...ry:Fault_Codes

[87supraman]

http://wiki.ross-tech.com/wiki/index...7/P1479/005241

Perform Short Trip in Basic Settings. Group 008 is commonly the self test for this system and may be activated Key On, Engine Off. If needed activate basic settings using [On/Off/Next] and pump the brake pedal.


If that all checks out OK, I would look for check valves along the vacuum hose going to the booster. If I get a chance I'll poke around mine today and see if I can locate any fail points.

[jschick]

yes have ross-tech, and the electric booster pump is working, and I forgot to mention I do get Multiple misfire codes so I was leaning towards the PCV system, but the misfires take a while to come up, the 2 lean at idle codes and brake booster code come up quickly after reset...... I was going to swap the purge valve just because I have one but don't think it is the cause, but since this is the wifes new SUV it is hard to get it from her to mess with........ and also I do have power brakes so the booster is working, but brakes are just a bit stiff, it does act like their is a vac leak in the booster someplace..... but idle seems perfect. Unfortunalty it isn't easy to trace the Vac lines to the booster since they dissapear behind the engine, or under the windshield cowl I was hoping someone would have a common fail point but havent been able to find any, except the PCV,

[clover168]

Sound like a carbon built up for me. I have the same problem with my12 3.0t . The dealership clean all the injectors and ports then all the code are gone.

The tech had to call Audi Canada for problem solving. Took them 3 days to find out the problem as well.

If your haven't had the carbon clean. I will suggest you to do that.

[jschick]

thanks,
I ordered the PCV so if that doesn't do it I will pull the intake and check for carbon, unless anyone else has any suggestions....

[dastt]

Resurrecting this old post. I had the same codes on my 4.2 Q7 and found that the rigid pipe from the vacuum pump that contains the check valve had cracked. This pipe runs in front of the right side air filter housing and gets moved for air filter changes. It probably could not take the stress over the 10 air filter changes so far on this car.

[flat12]

If the brake booster or related vacuum hose is bad - meaning a vacuum leak, that can cause a lean idle which may lead to mis-fires. I would definitely do as DASTT says above and check that hard plastic pipe that runs across the engine...there are several spots where it can crack and leak.