So I just picked up a 2000 A6 4.2L with 100k miles on it, great condition and runs strong. However, after about 200 miles it threw codes P1128 and P1130 (Lean condition on both bank 1 and bank 2). First inclination was a bad MAF sensor. Just replaced it two days ago and the dang code popped back up. Second thought is a vaccuum leak; however there is no rough idle or stutter/loss of power under acceleration that would typically go along with a leak.

I'm leaning towards replacing the O2 sensor(s) but what is the chance that both would go out at the same time???

Anyone have another idea as to what the problem would be before I go and dump $300+ on something that wont fix the issue?

 

I vote for a vacuum leak. Small vacuum leak will not affect idle. Sometimes it is hard to find the leak. Just replace a slew of vacuum lines and you will fix it. 5 feet of 5/32" diameter line will pretty much replace your entire engine bay. Cost is about $5 from any auto parts store.

 

Vacuum leak definately, find your vacuum check valves as those tend to fall apart after they hit 5-6 years old.

 

Also, i can't remember if this is right or not, but the secondary air lines connect to the intake post MAF sensor, so if those lines are leaking it would bring in extra air into the engine after the MAF which the O2 sensors would treat as a vacuum leak.

 

Thanks for the heads up. I went out an bought a new fuel filter and some of the tubing. Gonna try and replace all the lines this weekend. I'll keep ya posted if the CEL comes back.


well I changed all of the filters and inspected the vacuum lines (none seemed to be bad). but I do think I found the culprit. th clamp holding the intake onto the back side of the manifold was loose. nothing crazy but enough for me to wiggle the pipe around. remounted that and fired her up. No codes as of yet. If they do pop up I have the vacuum lines standing by to go on.
Thanks for the words of wisdom. I'm sure I'll be posting more on here soon

 

So i changed out all of the vaccum lines tonight and made it waaaay worse.

The car wont even hold an idle. Really rough and the CEL popped up right after I turned it on. Also, there is a secondary breather (i'm assuming thats what it is) on the top rear of the enging that is sucking in a TON of air. (circled in red) if i cover the inlet of it with my finger it will cause the engine to sputter. What the hell did i do wrong and how do i fix it? I changed out the lines one at a time to ensure they all went to the right connections? WTF?


And to make it worse, I'm on vacation and drove the car to Chicago. If I cant get this thing fixed I wont be able to drive it back to Tucson. If anyone knows a good mechanic in the area or can help please please shoot me a line asap.

 

Looks like the PCV valve, that doesn't have that much pressure. Duct tape that turd up until you can replace it, hell duct tape any line you hear leaking. If you're on the move i can't tell you how many times a roll of duct tape has saved my ***, especially when i was on the 10 going thru Indio CA and an intake line ripped. The ECU has adapted to running with a vacuum leak, once you plug all the leaks it will compensate and return to normal.

 

thanks man, im stationary right now for the next few days so its not a big deal. so that PCV valve might be the culprit???? would the ECU remember the running conditions of before even if i disconnected the battery? i'm assuming they would keep the old (bad) settings unless there was a hard reboot of the ECU.

So if I left it idle for a while and drove it around the country out here for a little bit it should "relearn" what the correct fuel/air ratio is....correct?

 

offhand, would you happen to know what that part I circled on my previous post is? I tried to get into the vagcom catalog....but it seems like it is down. Also, if you know of any other parts source that has diagrams and such I would really appreciate it

 

Just a thought, if you are going to get in and analyze codes, it is worth the money to get a laptop based code analyzer so that you can monitor sensors in real time to avoid costly parts replacements by guess. Until I got one, I had a pretty good little parts warehouse going. For example, when you can look at O2 sensor values, you can tell exactly whats happening with them. You can watch fuel trims in short and long term and so on. thsi would have saved you the MAF. On my XJ6, this part is worth $400. My Proscan cost $100....its economics. I maintain an XKR, an XJ8, a Volvo S70, A mini and now an A6, need all the help I can get.