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Discussion Starter #1
I have had a ball playing with my latest toy - the ElmScan 5 w/ the OBDWiz software - $28. (this is not a paid advertisment, I just think it's really cool, and so much cheaper than VCDS or a high-end scanner tool--of course you need a laptop, but most folks have that already). :thumbup:

I have been seeing intermittant P0491 and P0421 codes (low SAIS flow, low cat eff.), and was about to start throwing parts at the car (O2 sensor(s), combi valve), but instead bought the aforementioned scan tool. So, first I recorded the engine parameters during a cold-start:
lucy_pre-cat_o2.jpg
I was concerned that the O2 sensor, or the combi valve wasn't working, but all seem fine (O2 goes to the floor in both banks while SAIS is running). I disconnected the vacuum line to Bank 1 and tried it again:
lucy_pre-cat_o2_bank1_unhooked.jpg
and sure enough, the bank 1 O2 does not respond to the SAIS. So, both the combi and O2 sensor are working fine!

Yet, despite my glee over not replacing good parts ($150-$200 each), I still haven't found my smoking gun. I did notice some different looking results from the downstream O2 sensors, shown here after warmed up (idle, then 2000 RPM, then back to idle).
lucy_post-cat_o2.jpg
Any help explaining what this might mean are very welcome. :hmmm:

Last, I have the stats page:
lucy_stats.jpg
Only oddity here is the big difference in the long term fuel trim between banks, one lean, one rich - nearly 10% difference. I'm thinking vacuum leak, but welcome expert opinions - thanks!!! :driving:
 

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Lucy, those pix are too small to be able to discern what they are showing. I suggest you host the pix on photobucket or some other picture server, and use the img function to display them here.

I'd believe you have a vacuum leak. the V6 uses a lot of hard plastic lines for vacuum lines, and they get very brittle with heat and will literally crumble if you touch them.
 

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Discussion Starter #3
I'd believe you have a vacuum leak. the V6 uses a lot of hard plastic lines for vacuum lines, and they get very brittle with heat and will literally crumble if you touch them.
Did a vacuum check today (made a nice little rig out of some plumbing PVC pieces, an air pressure hose, and hooked it up to a vacuum cleaner with a big cork!). It wasn't the brittle vacuum lines this time (I have already replaced my combi valve lines), but there was a pretty big hiss coming from the valve cover gasket on the back side of bank 1 (the one that was throwing the codes). For now I gooped it up w/ RTV, but I will need a proper gasket & seals job soon. When I finished, I checked the intake vacuum at idle; was 16", now nearly 19", which matches what I see on my '03 sedan. (BTW, having a second car w/ the same motor is a huge help in trouble shooting, I highly recommend it! :lol:)

So I'm feeling pretty good about this one. If it goes a month without throwing a code, I'll call this one solved.

Thanks Jay!
:thumbup:
 

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I had a steering knuckle in my shed. Really!
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I only have two, since I sold the GTi. But to be fair, that was a transverse 1.8T and a different engine code than my two AEBs.
 
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