dcautomech

Makes sense. Once I get to the area of the sensor, I can double check the wiring and be able to check that after re-assembly.
Thanks for the info!!

AudiMick

Why don't you check the sensor using VAG.com? Group 17 IIRC

That sensor is a pain to remove, I really doubt carbon buildup would cause the sensor to react slowly.

dcautomech

Thanks guys. The sensor isn't really that bad to get to. Once the TB is removed, it's about 1" forward of the TB, just to the right of center. A 14mm box end and there you go. Once you break it loose, it will finger turn out. I don't really believe the Haynes manual does anything but make a job more difficult. It you want to do it right, get the original Audi Service Manual.
As to the sensor and checking it, The connector is just below the Vacum diaphram for the cruise control. There are two connectors there, it is the rear most connector. Under the boot you will find two wires, White/black and tan/red (or brown/red) DVOM connected to each terminal, (positive to white wire, neg to brown) and you'll read somewhere between 4.25 to 4.40 volts with the connector connected. I cheated a little and took the manifold vacum line of one of the solenoids (I didn't bring home a vacum pump)and touched it to the vacum line going to the EGR valve. Of course the engine started running rough, but the DVOM's voltage reading at the sensor connector started dropping immediatly indidcating good sensor operation.
As to carbon "insulating" the sensor, by way of design, I can see this happening. The line bore goes accross the bottom of the plenum with an intersected bore for entrance to the intake system. After looking at the sensor, I don't believe the exhaust flow does more then just reach the tip of the sensor. (direct heat from the exhaust may burn the sensor) Residual carbon build up, along with oil vapor that moves around in there could easily cover the tip of the senor.
On this model, the nut on the EGR tube where it enters the valve. Loosen 1/2 to 1 turn, remove the bolts from the EGR to manifold, and work the valve back and forth a couple times and it will lift off the tube without having to remove the tube from the exhaust manifold/cylinder head connection.
As to removeing the sensor, I would recommend a 14 mm crows foot. I mentioned that I used a box end, but this involves cutting the wiring to remove the connector so you can get the box end on the sensor. These wires CANNOT be soldered back together, so I used a type of "butt" connector to crimp the wires together and used a GOOD quality heat shrink to seal the crimp.
As to whether this has fixed my problem? Only a road test will tell for sure. Since all the functional and electrical tests of the EGR system passed, I am looking forward to a good repair.

davembryant

Does anyone have a detailed diagram or photo of the egr system for an A4 quatro 1997 v6

dcautomech

That is true and a good observation on your part. However if you haven't seen the EGR temp sensor and it's passage and position, then that is a valid question. Due to design, you can have an active EGR system and still have the fault due to an insufficient temp change with EGR flowing. Carbon can biuld up on, and "insulate" the temp sensor and allow the ECU to "think" the EGR is not flowing, even though it actually is.

dcautomech

On going now, it's been a year now since I've done my repair, cleaning the EGR passage and temp sensor port, and all is well. As to someone thinking that carbon build up could not insulate the temp sensor, I would have to say that statement is inaccurate since that is what has happened with my A4. Once I found the EGR temp sensor connector, I back probed the sense wire and observed the voltage change prior to cleaning it. Very little to no change at all. After removing and cleaning the passage and making sure the EGR valve itself was clean, along with the sensor and it's port/passage, then checking the voltage change with the system clean and seeing a nice voltage sweep tells me that carbon build up CAN affect the sensors operation. I had the same symptoms, checked the code, then checked the EGR valve operation, actuating the EGR solenoid and watching a vacum gauge, verifying operation. Then manually opening the valve and watching RPM change and idle quality deteriorate told me that EGR system was operating as designed. At this point I needed to know WHAT the ECU looks at to see if the EGR system is operating. You guessed it, the temp sensor. Happy motoring!!

96Cabriolet

Audi Enthusiasts,
I just executed the procedure outlined by vtraudt - almost, on my 96 Cabriolet, 12V (5-5-2017)
(Vdtraut - excellent write up, thank you)
the reason I did not follow it exactly is that I did not have the tool to undo the 22 mm flange nut from the bottom of the EGR valve - and this turned out to be to my advantage.
Instead I left the EGR installed and worked the cable clean out from the intake manifold side, with carburetor cleaner, inserting the cable into the passage just down to the EGR. After working the cable a while, I actuated the EGR to let the carburetor cleaner drain into the exhaust manifold. I did this 3 -4 times.
I reassembled everything as per the above procedure, and whoala! everything is working... And no risk of damaging the EGR or the fittings to which it attaches.
No codes, and better engine performance than previously.

Worked well for me, and if nothing else it's a lesser intrusive fix to start with - and if a no go for you, then you can pull the EGR.

Thanks, 96Cabriolet