I have done a lot of reading but this is my first post.

My wife drives an automatic 1999 A4 quattro with the 2.8 l V6. We recently moved from Maryland to Washington and the car was shipped across the country. Since we received the car several problems have come up. The most concerning, which started happening about 2 weeks after the move, is this:

Sometimes as you are coming to a stop (and I think more specifically when the car is downshifting from 2nd to 1st?) the car will just stall. It is not a jerky or abrupt stall and you might not even notice until you look down at the dashboard and see the RPMs at 0.
It does not stall every time you come to a stop. I have not figured out any pattern to the stalling at all. Some times it will go for a couple weeks without stalling and then the next day it will stall almost every time you come to a stop.

There is a check engine light on that I don't think is related but it may be. It is throwing a p0501 code which is a vehicle speed sensor code. The speedometer and everything are working fine so my theory is that there is just a connection that was vibrated loose in shipping.

Does anyone have some insight as to what might be causing this?

 

It is possible that vibration caused a sensor to fail but if you say you have CEL code referring to the vehicle speed sensor, my bet is on the sensor itself.

The vehicle speed sensor is mounted on the passenger side of the transmission I believe. The sensor itself is not that expensive, about 30-40 dollars online.

If you don't want to replace the sensor right away, you can always try removing it, cleaning it and putting some di-electric grease on the connecter terminal and give it a shot.

 

Depending on the engine, I'd say Idle control valve is shot or needs cleaning. Same symptoms I had; the idle would drop right to zero and stall when I came to a stop.

 

I'm pretty sure that the 30V engine doesn't have an ICV like the 12V engines. Also, the vehicle speed sensor in an automatic trans car is internal to the trans, and the wiring joins the other speed sensors, temp sensor, and solenoid wires at one connector. The OPs description of the speedo working seems to prove the VSS is alright.

I'd clear the code, and see how long for it to reappear. Are you using VAG-COM to check this? A general-purpose code reader might be missing some important details. How about the trans module- any fault codes there? A lockup clutch fault might stall the engine.

 

Audi must have decided to make our life a living hell by interconnecting all those sensors and solenoids.

 

I have a general-purpose code reader and have cleared the code multiple times with that and it just comes back on after a short amount of driving. I don't have vag-com but was able to borrow a cable a little while ago and it told me vehicle speed sensor: invalid signal or something like that.

Something I forgot to mention is occasionally the CEL will turn off all on its own but has always come back on usually within the same day.

 

I have a 98' A4 2.8 Quatro and it is doing the same thing. Just got this car a week ago off craigslist and since then my head lights have stopped working and now the car is stalling randomly at stop signs. Its worse and more frequent the colder it is. I have no idea why its happening. Are your head lights and electrics working fine?

 

Off the topic of the original post, but look in the DIY area and the process for fixing the headlight switch - that should bring those back.

 

Check your MAF. If it runs fine any other time, and starts right back up, I'm going to take a stab in the dark and guess it's your MAF (mass airflow sensor). There's photos of where it is in the DIY forum, you can test it by unplugging it while the engine is running to see if it makes the car run better or worse.
Could also be a vacuum line with a little crack in it etc...

But if the Check engine light goes on and off, it's pointing toward the MAF.....

It would be best though to get your car scanned with the VCDS software (VAG), generic or non audi scanners only read the main ECM codes, not the other modules...then you'll get a better idea of where the issue lies.

 

I've been told to unplug my MAF and I'm wondering two things. If its that shouldn't my check engine light be on? Also when you say unplug the MAF while the car is running do you mean run the car that way or just let it sit and idle?