MegaMumms65

Hey all!
I have a 1997 A4 Avant with the 1.8T (AEB) engine and a manual transmission. It is a regular fwd, no quattro. It's a great car, but there is one issue that recently popped up.
It started when the battery drained after the car had sat for a little to long. What happens is that when the ignition is turned on, the speedometer needle moves to 0 and just stutters in place. This does not change when the car is started, meaning I have to drive without knowing how fast I'm going. In addition, the tachometer does not move at all, just stays still at 0. What is odd is that all other instrument work, like the temp gauge, fuel gauge and all the warning lights. If the car is started with the speedometer not working, it does not start working as long as the car is turned on, no matter how long I drive for.
To add to the confusion, there are two things:
1) Sometimes, both the speedometer and tachometer work without issue. Some days they work every time, on other days they don't work even once. There does not seem to be any pattern or logic to it. When they do work, they work as long as the car is turned on.
2) There are no fault codes, and when I plug my computer with VCDS into the car, I can actually read both the rpm and speed no matter if the gauges currently are working.

My theory is that it has something to do with the battery draining, since I drove the car a lot of miles before that incident without any issues. I am however not very familiar with how instrument clusters work, so I am unsure how that would work.

Beside this issue, the car runs great without any other major issues. I have tried looking for other threads with the same issue, but I never managed to find any with solutions to the problem. If anyone knows what could cause this or knows a thread that solves the issue, I would greatly appreciate it if you would share it! I will include a clip of what it looks like in case my explanation was unclear.
Thanks in advance!

Cybersombosis

Have you scanned for any codes? If so what are they? I suspect it’s a engine speed sensor located at the driver’s side output shaft and possibly a corroded connector since it’s intermittent. You will have to take off the driver’s wheel to access it. Unplug it. If you have a small tipped file, insert that into the connector to clean it and take some dielectric grease to protect it from corroding again. Push the release clip in and insert and pull off the connector multiple times to scrub away the corrosion and hopefully that will solve your speedo problem. Don’t know about the tac issue but maybe solving one will solve the other.

MegaMumms65

Thanks for the response!
I should have mentioned it in the first post, but I actually changed the engine speed sensor a while back because of this issue. Did not have any effect on the matter, and since I was able to read the speed at all times through VCDS I concluded that it couldn't be the issue.

On a positive note, the issue has now been solved. After some investigating, I concluded that the speedometer was defective. What would happen is that it would try to reset to 0 when ignition is turned on, to initialize the needle i suppose, but never being able to reach 0 and therefore endlessly stuttering at just above 0. With the glass removed, I could simply push the needle up (counter intuitive, I know), which immediately stopped the needle from stuttering and made the tachometer start up.
My guess is that when the key was turned with the battery almost dead, current was able to flow in ways it shouldn't in the cluster and ruined something. I took a peek inside the cluster, but found nothing obvious and decided that trying to fix it would be above my skill level.

So the fix was to simply replace the cluster. I was able to find one for pretty cheap and it was a breeze to install. Works every time now without issues, hoping it stays that way. Maybe it is a fixable issue, but I will leave that up to someone more knowledgeable in the subject.