2000 A8L stalls coming to a stop/ put in gear
 

Facts of the case:
Car drives fine, shifts up and down so smooth you don't even notice the gear changes, even on steep hills.
Put it in reverse or drive with your foot on the brake, stalls about 70% of the time, less often in high idle from cold start.
If you put it in gear and go almost right away, it's fine.
When coming to a stop from street speed, will shudder, idle drops, and often stalls out.
When it does not stall, it lurches as if you suddenly slammed on the brakes, then returns to normal idle.
I notice that if you are in a parking lot going slow enough to keep it in first, nothing goes wrong, feels normal.
Using TIP mode makes no difference.
Put it in neutral at a stop, and it doesn't stall, but often does when you put it back in gear.
I've had it at a highly recommended shop that specializes in Audi/VW. He checked fuel pressure, vacuum, throttle body, trans fluid, hooked up the computer to it, and yadda yadda. He was forced to admit that he does not know what the issue is. Says he thinks its electrical. I'm not so sure. Feels mechanical to me.
My next step is taking it to a transmission specialist, unless there is ANYthing else I can try at home?
Meanwhile, my A4 continues to run for it's 5th year in my service with not a single engine issue to date. Manual trans, of course.
Cheers!

Fuel filter? weak pass side fuel pump?

+1 for replacing the fuel filter. My fuel filters usually last about 30-40K miles before they become pretty restricted. It really depends on the quality of the fuel your buying.

In addition, vacuum leaks are a very common problem which can really screw with the idle. The car has two vacuum tanks, one each located just above the side marker lights in both front fenders. The tanks have a hard plastic tube that is about 18 inches long and then it connects to rubber hoses just behind the headlights. I mention the tanks because my hoses cracked at those unions. If any of the hoses are original, it's best to replace them all. There are at least 5-8 different tee fittings for cracks in the hoses to develop. Don't forget about your diaphrams and associated tubing at the front of the motor used for changing the intake plenum door position.

Also, do you have any idea if your crankcase ventilation valve is working properly? It's the 4 inch black plastic, UFO-looking thing at the back of the engine. If you let the car idle and pull the oil dipstick, the engine usually speeds up a little to account for the air leak. Normally, once you pull the dipstick, you might hear a horn like sound coming from the rear top of the engine. It's not a normal check, but if the engine doesn't change idle speed and you don't hear any sound, your crackcase breather valve could have a small tear in the diaphram.

Check the rubber hose that leads from the lower part of the air cleaner box, back to above the rear of the engine next to the firewall on the passenger side. Heat from the exhaust will cause the hose to deform and develop a hole almost directly above the passenger side exhaust manifold.

How many miles? What's the history of the vehicle?

MAF, CPS or maybe the fuel pump would be my guesses. A restricted fuel filter would be more of an issue under high load.

Clean the MAF, cheap and easy. If it's the fuel pump you'll soon be broken down on the side of the road so that'll reveal itself. CPS can be an issue of the motor mounts are also shot and the engine shakes like a wet dog at idle.
Watch the tach when it stalls, if there is no crank signal the tach will drop dead.

Thanks for the input, gents. There have been a few developments since then. The PCV thing makes the goose noise occasionally, but hasn't in a while. However, I am thinking the issue is electrical/ecu related. Here's why: Recently, the car wouldn't start, crank but no start. Had it towed home, then it started for me. Drove it for a minute, but it eventually sputtered out and stalled, had to have it towed like 800 feet. Lame. Anyhow, while tinkering with it, I swapped in the spare ECU just for kicks, I knew it wouldn't work without being coded, but what the hell. Of course, it didn't start. When I swapped the original back in, car ran great. NO stalling, no CEL, just perfect. Next day, start it up again, and it's back to stalling, sputtering, and the instrument cluster just dies out, all lights off, all needles drop. I sent my spare ECU to get the IMMO deleted. Didn't work, I put the key in, and it seems to just keep resetting: cluster comes on, then in s few seconds dies out, and lights up again as if I'd just put the key in. And it will crank all day. but not fire up, or even kick over. So, I put the old ECU back in, and the car fired right up, and drove like new, no stalling, no CEL. I drove it for a bit, shut it down, restarted it several times, ran fine. 24 hours later, started it again, AAAAND back to the sputtering, flashing IMMO light, and stalling when put in gear. Also, the original ECU smells slightly of burnt PCB board. I'm thinking if I can get the spare to work, all would be well, but I already blew $160 on that, and now I have to go to the guy who did it and bitch. I'm willing to send both ECUs off to be tested and fixed if possible, but I need a good verifiable recommendation, as there seem to be many options, and I already used one bad one. We already bought her another car, so time is not an issue. The A8 is just taking up space for now, but I'd love to get it working.

Also, 167000 miles, I bought it as a non-runner from an old man who had been throwing parts at it. I put a new battery in and it fired up and seemed ok for a couple weeks, then all this stalling and cluster death started. Also, the plenum drains had clogged, so there was a little water trickling onto the floor on both sides.

Electrical. Start at the beginning. Battery terminals good, clean tight, no corrosion. Imagine how funny it would be if it all came down to a loose ground cable on the battery. When it dies at the cluster, do you have power anywhere else. Check the positive junction inside the right wheel well.. They have been known to corrode and cause total power loss - not exactly your symptoms.

The Instrument cluster, not the ECU, is the conductor of this orchestra. The cluster houses the Immobilizer function. If you were able to get the secret 4 digit code out of the cluster, you could then use that code to pair a new ecu to the car with VAG-COM. I bought a cheapo chineese gizmo to pull the 4 digit code. It works, sometimes - even their coding is sketchy. Anyway, there is another way to pull the code right out of the hex-file with a vcds lite cable to the OBDII port and some free software. There is a writeup around here somewhere. Used Clusters and ECUs are cheap used on car-parts.com, usually $50 or so.

However, the cluster is NOTORIOUS for being temperamental. Often the "fix" is just to pull, disconnect, then reinstall the cluster and all is right with the world. Audipages.com has a writeup. Upgrades>Interior>Dash Rings, will show you how to remove the cluster. Say a prayer of thanks to PaulW for hosting it. Or send him beer in...Illinois? The physical act of re-seating the connections knocks off a little oxidation, and then the contacts are all clean enough. Did I mention electric contact spray cleaner? Be careful when doing this. I'm hamfisted and managed to bend a pin or 3 on the back of the cluster when reinstalling.... hmmm that doesn't look right... and spent a bit of time with a tweasers straightening everything out. Once, I actually took my cluster completely apart when I thought I fried it while welding a trailer hitch on the car. I pulled the original and Paired a new used one with a few more miles on it. For laughs, I took the old cluster apart, unplugged everything, ribbon cables, internal power supply, etc.. Put it back together, re-installed it and it has worked fine ever since.
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If there was enough water to reach the floors, then your computer had definitely gotten wet at some point. You might also want to pull the passenger side floor mat. access the relay box under the inclined portion of the floor - 3 screws - and pull and check all of the relays. High and dry in there? Any evidence of water intrusion? There is a combination relay that powers the ECU. For that matter, you could easily open up the ECU - it's just a board sandwiched between two sheetmetal sides - and check for arcing, scoring, corrosion, leaking capacitors. Basically, treat it like a flood car. Open, inspect and clean the connections in those 2 areas especially. Electric Contact spray cleaner is your friend.

You could have corrosion on the contacts of the Main relay in that footwell box ( a little far-fetched). The plastic covers on the relays pop off without too much fuss. Inside, you'll find something that looks vaguely like an old fashioned electro-mechanical doorbell - a coil of wire around a magnetic core that, when energized rings a bell, or, in this case pulls a large set of contact points closed, or open, or a bit of both depending on the function of that particular relay. Inspect the relay contacts for pitting or corrosion. Crazy stuff like that. Power up the car with the individual plastic covers off of the relays, and you can see how they work. Or, with the covers on, remove the relay, slide it in with the ignition power on and feel the click in your hand.

BTW, take your honking PCV valve off and wash it out with warm soapy water in the sink. Run water through all the openings until it runs out clean. Reinstall, gtg. If you are brave, you could carefully disassemble it and inspect that the diaphragm is not torn. I break plastic tangs, so I didn't. Aftermarket PCVs are random, but mostly crap. New OEM is stupid money. Cleaning the original should work just fine provided the diaphragm is not torn. It isn't, just clean it.

Usually, the symptoms you describe without the freaky cluster behavior, would point to fuel pump. And you could have multiple issues. But the Cluster flashing IMMO is a cluster problem, or a cluster power delivery problem. Your key has a transponder pellet inside the key head. It looks like a tiny Tylenol time release capsule housed in glass. The field reader around the ignition barrel reads the pellet and the instrument cluster decides if this is a key that is allowed to start the car. This has NOTHING to do with the door lock remote radio transmitter at the other end of the key that pairs to the alarm system. Separate system entirely. After checking the obvious battery connections and grounds, I'd pull and reseat the cluster.

Do you have VAG COM or even VCDS-lite, a code reader... a multimeter... anything? If not, you are pissing in the wind, and that consumes time money and patience fast. Spend a little to save a lot.

For instance, at this age and mileage, you might even read intermittent misfires and have failing ignition coils. It's inevitable. VAG COM will tell you which one(s). Replace them with cheaper better and redder red-top coils.

If I was working blind without VAG COM, and could only go on what I observed, I'd check and clean all connections and I'd definitely pull, clean and reseat the instrument cluster.

Good luck.

I just read your first thread. Water entering through the fresh air inlet in the underhood cowl area poured into the hvac ducts. The ducts directly over the radio leaked water onto the radio. The radio fuse blew. You will not be able to read the OBDII data, the K line, until you unplug the radio, or replace the fuse at the back of the radio if the radio is still good. It likely is.

And the ECU smells burnt because when the cowl flooded, water entered into the bottom of the electronics box and created a bunch of short circuits. Mine got soaked in a heavy downpour in 2004. Took out the TCU, ECU, blew the radio fuse, water in the ductwork, water in the floors, even cooked my fuel pump and a couple of coils.. sound familiar. My ecu worked after drying it out but had a persistent altitude check error. I replaced it with a used one that the dealer paired to the car. You might want to clean the cowl center drains and the inner fender nipples - that's four cowl drains total. Probably clogged with leaves and dirt..

First, thanks for taking the time to reply so thoroughly. And I am remiss for neglecting to mention a few things: I do have a scanner, and the only code I'm getting is P1185. No CEL, and the scanner says no codes, but when I tell it to read codes anyway, that's the one I get, which I believe points to a missing signal to the cluster from the ECU (?). I got VCDS lite and a cable, but have been unable to get it to communicate, but that's probably just an issue on my laptop's end, incorrect port assignment or something. I haven't looked to far into that, admittedly. When we got the car, the radio was dead, and I could not read codes, but I pulled the radio, replaced the blown fuse, and all was well. The PO even had the radio code on a receipt from the dealer, so I was able to make it all work again. Of course, it's back in safe mode, but the fuse isn't popped now, so I can get codes. The passenger floor mat has been off this whole time, and I check it every so often for puddling water. It's a little damp, but not getting worse, since I have made an effort to get a hose down in the plenum and unclog the two drains (Incidentally, right after we got this car, the plenum drain on my A4 clogged, and I had to pull the battery and unclog THAT one too. Must be contagious).

Also, I have opened up the ECU, along with the donor unit, just to do a visual comparison. There was some obvious, albeit light, oxidation around the pins on the Eprom chip. I ever so gently brushed and scraped it away, in case some of the oxide was conducting between pins. I used a magnifying glass and a teeny pick to scrape along the traces on the board as well. When I put it back in, the car ran fine, started up right, no stalling, no immo code, Yay! However, I am not one to count chickens prematurely, so I waited until the next afternoon, and all the symptoms had returned when I started it up again. So the only consistent behavior I'm getting is when I take out the original ECU and put it back in, the car runs fine...for a few starts.

Anyway, I will look into the condition of the cluster and its connections. It's a distinct possibility, and I'm pretty sure someone has been in there before, there are signs that the steering wheel has been off, and the wiper mechanism has been tampered with. Again, thanks for your time (all of you) and if you have any more thoughts, I'm all ears.

EDIT: Argh, one more thing I forgot to mention, PO had installed a new fuel pump, but likely one that is generic aftermarket. The mechanic I took it to said fuel pressure is "spot on," however. I still don't trust the PO's handywork, but it is something that bears mention.

Ok, pulled the cluster, zip ties were all in place, so it likely hasn't been out. Cleaned the connections, put it back in. Car starts right up, runs fine, doesn't try to stall when put in gear. BUT the cluster still goes out, and here's the curious thing: The CEL is back on, and when the cluster dies, the CEL stays on for a few seconds, then it dies too. In a few more seconds, the cluster comes back on, in this order: Lights and then in a few seconds, the needles on the tach and fuel level come on. IMMO light is flashing too. Makes the chiming sound as if I'd just put the key in. None of this affects the engine, it continues to run like nothing happened. There is power to the rest of the car when the cluster dies, the vanity light and wiper still work when it goes dead. I'm thinking a new (well, different) cluster is the next step, but I'm tempted to just open this one up and reassemble it like you did, not much to lose at this point, and I've definitely done work like that before. You mentioned an internal power supply. Is this a little 5v linear reducer for the circuitry inside? I've had processors go bad (not in a car) and it was determined to be the 5v internal transformer. I can see this being a likely culprit, as the car had sat for some time with an entirely too small battery that had drained to 7v, and I've found that too low of a voltage can do more harm than too high.