Found this key fob from a post on Audizine and purchased off eBay. Works great except the trunk button doesn't do anything. I'm just glad i finally have a spare set of keys.... only took me 9 years to get another fob. Just for the record, the B5 line does not use a "immobilizer chip", so if you get one of these, don't get suckered into paying for that to be "programmed". The locksmith I went to get the key cut was convinced it would not work, but I got to show him that he was wrong.  

• Audizine Thread: https://goo.gl/j4mMpH 
• eBay Link: http://www.ebay.com/itm/131224505466
• Audi Sticker: https://amzn.to/2q9ouKR

And a little videos to show it really works:

Before you start, make sure you have at least two keys that can manually unlock/lock your car. You can not program your key fob with only one key.

Clear your Key Fob Memory Positions
Our B5 S4 can store up to four key fobs for wireless entry, but to simplify the process of programming it best to start with a clean slate.

1. With one key fob, insert the key into the ignition and turn to the "on" position. Take note we are not turning the engine on, just the one position.
   
   
2. Exit your S4, close the door, and insert your second key fob into the door lock.
   
   
3. Turn and hold your key clockwise to "lock" you car.
   
   
4. While still turning the key to the lock position, press the unlock button on your key fob 5 times. Wait one second between each press.
   
   
5. Wait 5-8 second, take your key out of the door and press the "unlock" button on the key fob once more. 
   
   
6. Open your door, take your key out of the ignition, and verify all key fobs no longer wirelessly lock/unlock your S4.

Re-programming your New and Old Key Fob.

1. With one key fob, insert the key into the ignition and turn to the "on" position. 
   
   
2. Exit your S4, close the driver door, and insert your second key fob into the door lock.
   
   
3. Turn your key to the lock position, hold, and press the unlock button just once.
   (This action initiate the key to be recorded to the 1st memory slot)
   
   
4. Take the key out of the door, wait 6-8 seconds and press the unlock button on the key fob once more.
   (This action will save/record the new key)
   
   
5. Open the door, take the key out of the ignition, and test the key that was previously in the door to make sure it wirelessly locks/unlocks.
   
   
6. Now we need to program the key that was previously in the ignition. Take the key that was in the door, insert into the ignition, and turn to the "on" position.
   
   
7. Close the driver door, and insert the other key fob into the door
   
   
8. Turn your key to the lock position, hold, and press the unlock button two times with a 1 second pause between each button press.
   (This action initiate the key to be recorded to the 2nd memory slot.)
   
   
9. Take the key out of the door, wait 5 second and press the unlock button on the key fob once more. 
   
   
10. Open the door, take the key out of the ignition, and test all of your key fobs.

Troubleshooting
When I first attempted this I noticed I could only get one remote working at a time. That is when I realized I was saving one key fob in the same memory slot. Take careful attention to step #3 and #8 as you are selecting which "memory slot" you are recording the key fob too. The number of times you press the unlock button will instructed which memory slot is used. 3 presses will go to memory slot #3 or a single press would go to memory slot #1. Remember, there is only 4 memory slots, so don't go crazy and press the unlock 5 or more times as that will clear all key fobs and you will have to start over. 

New picture with Audi logo

It's been a busy month so far with the S4. I did just finished installing the 2.0T Coil Conversion ​kit I got from ECS Tuning.

Performance Differences? 
In summary, no, not really. It kind of feel smoother when accelerating past 4000rpm to redline. I did replace my spark plugs at the same time, so whatever I feel could simply be fresh plugs. The good news is I'm able to run a larger gap with my spark plugs. I left them at the stock 0.028 inch gap and no misfires. Before if I ran anything over 0.024 inches I would get misfires in cylinder 6 at WOT. MPG does seem to be 1-2mpg higher as my 30min test drive on the highway shows 27-29 MPG. Again this could just be the news spark plugs. I do continue to feel slight shudder every 5-10 seconds when the car is at idle, but I have a feeling this is likely because of a vacuum leak around my intake boot.

(WOT = Wide Open Throttle)

Thoughts on the kit?
It certainly feels over priced and I knew that from the start, I just didn't want to deal with making a wiring harness from scratch... So yes, I'm paying extra from convenience. As well, the extra wiring kind of makes the engine bay look messy. I'm sure with a few black zip ties here and there I could clean it up, but I'll do that a few weeks from now once I'm confident that everything is working ok. I do really like the 1 piece mounting plate for each side of the engine. I pick the black color as I really don't like a flashy engine bay. The mount just look more OEM in one piece vs some other setups that have a separate mount for each cylinder. As for the wires they all look very OEM. The once thing I don't like is the length of the ground wire. It seems like it should be 1-2 inches longer so nothing is pulling on it. As the wiring is routed at this time, I'm sure a year from now I would be working on fixing broken ground wires.

How was the install itself?
ECS on their instructions claim this as a "easy install" and I do agree with that. The hardest part, as with everything on this S4, you spend more time moving stuff out of the way than you do with the actual installation of whatever part you are working on. Remove airbox, relocate coolant reservoir, remove old coils, install 6 bolt per mounting plate, press in the new coils, connect the wires, re-install airbox/coolant reservoir, and finally go for a test drive. So it's a rather easy install. I think it took my 2.5hrs to complete but I was going at slow pace.

Would I recommend it?
I would say that it is too early to tell. If you are bored and want to replace something with something "newer" because you got the itch... sure go for it. If your stock coils work without issue, then no, this would not be worth it for you. For me that cylinder 6 misfire is the main reason I replaced this as I wanted to see if it would help correct the misfires that seem to come back every 12-18 months. 

Wow I forgot what a pain in the butt the fuel filter is to install, but it is in there. The last time I replaced it was back in July 2008, so I've put about 80k miles on the old one since then. I think it took me about 2.5 hrs to complete, but thankfully it was mid 70's here aka perfect car maintenance weather. After the install I did do the "blow" test on the old filter (sorry I know that doesn't sound right) and it flowed with no issues. The theory is if you can easily blow through a old filter then it is still good. I'm rather shocked that it was still good with 80k of miles on it as some have said to replace this every 25-50k miles. If anything that just shows the Costco Premium gas I've been running for the last 8-9 years is very clean. 

Anyway, 2.0t Coil pack conversion install still in the works, I just wanted to do all of this in stages so I could tell if there is any difference in performance. At this point, no difference in fuel economy or power with the new fuel filter.

Sorry this is a teaser, but I just got my 2.0T Coil Pack Conversion kit from ECS Tuning. I hope to have it installed in the next week. I know some people say this is overkill or unneeded, unless you are having issues with your coils. Well last week my cylinder 6 coil died, again. I've lost count how many times I've had issues with coils on this cylinder. I willing to see if this helps at all. I know expensive test, but it's worth a try. Well keep you all updated once installed and tested.

Also got some other parts to install:

• New fuel filter
• Spark Plugs​

​I'm pretty sure the S4 will be running very smooth after all of this is installed.