Man, my A4 was getting around 15.8 mpg in city commuting (and it's a 5 speed and I usually shift around 3,500 rpm!) With gas almost at $3.00 a gallon in SoCal two weeks ago (and around $2.75 a gallon now) I wanted to maximize my mileage.

I ordered two pre-cat O2 sensors online ($288 including shipping) and installed them. Wow, it was an easier job than I thought it would be. I got both installed in under an hour.

The results? Well, on half a tank, I saw that my commute mileage went up to 19.8 mpg! Better yet was that my performance increased slightly, especially at the higher RPM range.

I guess I shouldn'thave skimped and should have gotten these replaced long ago! (I have 172,000 miles on the car now.)

Bob

along with a new exhaust and...*gasp* possibly a new tranny. I'm starting to feel a little shudder when I shift into 3rd and 4th at high rpms on the gas. Cheap fix I'm sure.

I bet generics spliced in would cost more than they save in decreased fuel economy within a year.

No flames please, I'm in no mood to defend my personal opinion. :) If you want evidence, do a search, it's been covered.

Plug-and-play. I thought about the generics also, but I don't want to re-work anything if I didn't have to (i.e. have a splice come apart, etc.) so I decided to just buy Bosch O2 sensors with the harness and be done with it. Easy job!

... I think it's the tranny mounts and snub mount. I'll be replacing those next! Allroad tranny mounts and Mance's snub are what I have planned.

It is so subtle that I doubt any of us would notice it. (It does degrade over many thousands of miles after all.) But I had always wondered why my A4 would rev so slowly for the last 1000 rpm in 2nd gear. It was the fuel mileage that really got me thinking about changing the O2 sensors. After the change, the car feels noticeably stronger and mileage is better. I wish I had done this a LONG time ago!

I still have the shudder :( . It shifts much smoother though. I recommend the upgrade but it probably won't fix the tranny problems

They are the same o2 sensors that you can buy with the connector - just without it

The problem is in the splice, not the sensor.

The plastic ties were harder to undo, but a little patience and you can undo those without having to cut them. If you use the special O2 sensor socket and a 12 - 14" extension and U-Joint, you won't have any problems. Easy to reach directly below (just move radiator overflow tank and oil breather hose out of the way on the driver's side, intake plumbing and oil breather hose on the passenger side.) Should take about an hour.

mance was saying something at one point in time that it might have something to do with the plate switchover in the IM. Something about it sometimes during high rpm shifting makes it shudder a lil. Mine does it... I'll keep ignoring it until it becomes a problem ;) haha

and as far as I am concerned - they are running great. I thought the o2 sensors that didn't work were the VW ones or something.

I thought for sure I was experiencing the early signs of another big dollar repair. I guess I can blissfully ignore it too now! I have new engine, tranny, and AA snub mount so I know it's not that.

arise when you're using the S3 MAF, which led to the 0-rings to adjust airflow and prevent CELs. I might be off base here... ;)

Sorry for using you a lot Mr D ! Thanks for all the info on your site as it so far has helped me with my snub, allroad mounts, o2 sensors, t-belt, and loads of other ideas for future projects!

until the car doesn't move, or makes horrid noises in gear I won't worry about my tranny ;)

besides its not broken just not working properly

if it could cause problems i??

Not that it means that was good for the car.

then

I suppose it's less than ideal if one O2 sensor function flawlessly, while one's lazy.

i was thinking of putting them in as i got them maybee a month apart but if i might mess somthing up i would just wait till i have them both.. since i got to get two i want to space out the payments on the pricey babies... since i am not planning on going the slpcing way this time..

If you don't have a CEL at this time, wait till you have two new sensors and install them at the same time.