MP4.2+6.0

April posted in the last week or two about a recall involving Volvos that got me thinking about the Audi tranny clunk problem. I searched the archives for it just now, but search seems messed up. My car is a 2000 4.2.

The "clunk"--For those of you who either suffer the issue or have seen it posted over the years, I'm talking about the situation where the tranny makes a sudden very severe shift under slight acceleration, usually from slow speeds. The jolt is severe enough that it feels like the car was lightly rear ended; passengers definitely notice it and the tranny often goes into limp mode where the tranny inst. panel display lights up in reverse. It only happens very occasionally to a lot of people, in my case sometimes less than weekly, but once in a while repeatedly. The problem cannot be accurately replicated based on throttle position, rate of acceleration, etc., so getting a dealer or anyone to look at it is a wild goose chase. In my case it happens at low speeds, either in rolling stop scenarios (where I suspect the tranny has not gotten back to first yet automatically) and I am then using the throttle lightly to speed up, or when I am accelerating at a modest rate then press down just a bit more in everyday stop and go suburban driving. It doesn't happen in hard acceleration situations. If it happens several times in short order, sometimes it throws the CEL. The fault codes read things like gear ratio incorrect (duh!), implausible signal and other similar codes that also overlap the typical MAF warning flags. People have reported the issue off and on for years, and you can find it in the A8 C2 archives going way back. It is also reported in 2.7Ts and NA V6's, so it doesn't seem unique to the V8 tranny. I've never heard anyone get to the bottom of it definitively.

Prior fix ideas--Over a couple of years I changed out the MAF under the recall/service deal and that helped a lot--it went from what deteriorated to a semi routine problem to once in a while annoyance. I periodically do the throttle adaptation/recalibration/learning routine, which seems to cure it for a while but over a month it relearns its bad behavior. I've also changed the tranny fluid and filter once, which seemed to help. Before April's thread, my suspicion was one of the solenoids was acting up in the tranny valve body. You can get those as individual parts from the dealer, but if you look at the tranny shift stuff in Bentley, if it involves first gear it could be almost any of most of the valves and solenoids that add up to like $500 in total, plus the labor, fluids, etc. and no guaranty that's the solution. For reference at times I've been stock tranny code, at times 00032 and 00022. I've also used a GIAC tip chip but also have an unmodified TCU. From swapping back and forth, I've concluded none of that stuff is the root cause or has much impact on the probem.

The new idea--Anyway, back to April's thread light bulb. When I waded through the Volvo recall article link, it discussed the electronic throttle and that the engine throttle component (rather than the pedal side) was implicated. I had wondered about the gas pedal electronics previously since I believe the problem is invariably somehow related to throttle movement (not just position), but never thought about the engine side. My prior experience with the MAF also caused me to think about contaminants in the intake system. Side note for any of you still wed to K&N oil type filters--on top of reported MAF problems this all suggests another indictment against them. The Volvo recall sounds like maybe some pretty bad problems with power loss, etc, but for anybody who has experienced limp mode in a V8, without the torque converter lock up and in a fixed third or fourth gear and who knows what on engine timing retarding, 300HP feels like 50 and your average Neon can outrun you as the engine revs loudly. Not impressive, and you always get the "look" when you restart the engine to clear the limp mode, and get the added "what's up" factor at night when the headlights go off and on.

So what to do for the new possible fix--I unclamped the big rubber elbow from the throttle unit and the black plastic straight tube clamped at the rear of the motor where the intake plumbing heads into the manifold. You can't really see in the huge throttle opening without a mirror but you have good access to the throtttle unit and can see the electrical plug connection. I got in there with a clean cloth and some brake cleaner and wiped it all out for about 10 minutes--the throttle plate and the bore several inches deep. I used brake cleaner rather than carb cleaner because I wanted a rapid dry no residue solvent to minimize contamination issues with the O2 sensors. High concentration rubbing alcohol might be another choice (used by people who have tried cleaning the MAF hot wire component). I didn't see any vacuum ports present that you would have to be careful to avoid clogging. I found a fair amount of very slightly oily and carbon type deposits--the kind of routine stuff you see in an intake with normal use. The suction point for the highbrow named and priced PCV valve unit (aka the vacuum valve, the suction valve, the suck body, etc)that is getting reported as problematic in 2.7Ts especially is right on the rubber elbow in the 4.2. By the way my 4.2 is the earlier ART engine, and I'm not sure the later engine has that same suck body plumbing. You might think it would be inconsequential, but figure at light throttle there is a lot of air disturbance around the throttle plate where minor discrepencies can play with the air flow, or maybe the gunk is just hanging up the throttle plate for for a tiny fraction of a second.

Punch line--a week or more has passed and with no throttle adaptation even, the clunk remains banished. I've tried goading it with the throttle type moves that could make it act up without incident. Like I said, you can't recreate this problem systematically, but by about now I would have expected it to flake out if it was up to its old ways. Anyone else with the issue want to try and report back? 15 minutes, a screwdriver, a clean no lint shop rag and a little no residue solvent is all it takes.

Stoney

Is it an easy swap? I've avoided the chip due to wanting to stay stock for my extended warranty, but if the swap is easy I'd be interested. What is the total cost?

Potomac-Greg

... seems to fix it, and then again nothing seems to fix it.

I have not had a real "clunk" since getting my tip chip about a month ago. Of course, that means I'll get it today. It also went away after a trans flush, but then came back.

I've never had it go to limp mode, but you do describe the symptoms very well.

MP4.2+6.0

You might be able to find one if you have your part #. It's on the outside of the TCU, but IIRC it is also on the VAG-COM screen when you open the controller. I typed the raw number into Google together with "Audi" I think, and it came up with a few junk yards. The search may also yield a back door into a GIAC list of all the audi ECU/TCU part numbers; I found mine anyway. I think I also poked at car-part.com. After a bit of e mail false starts, I found one w/out the endless calls to junk yards. Did it a while ago, but my guess is $150-200 from a bona fide place with a 30 day plus return guaranty if it is DOA. From there, you get it chipped at a GIAC dealer at their std. pricing (all this assuming you can't find a used chipped one complete; virtually never seen I think, at least on a 4.2; maybe on an S4).

The TCU is under the front passenger carpeting--remove the side kick panel, pull up the plastic door jamb trim, pull away the carpet and pad, and it's in a black plastic outer box, held by just a couple unpainted screws. There are no security screws, paint or anything. Just plug and play; no adaptation either. The only way to tell is if you crack the box open, you'll break off the metal tabs. With a spare of course you can't ever see it. If you are in the Bay Area as I recall, it's probably Dynospot Racing and you would likely want them to do the install so you know it works and you just keep the known good box on hand.

Note this is different than the ECU where the later ones have the "chastity belt," you have to deal with the immobilizer in later years, I dont' think the CA smog machines can read it off the OBD connector, etc.

Even with it in, it's never been obvious when you scan the TCU anything is different; part number comes up, it accepts the 00022/32 coding, shows fault codes, etc.

Jeff786

Gentlemen,

I have an A6 2001 4.2, I just have 101K miles, I was driving the other day business as usaul and one of the main street was blocked, so I took the side street and quickly went through 4-5 blocks with stop signs at each, at my sixth Block I had this cluck for the first time, it got worse in the next 5 blocks and by the time I got home---complete limp mode bad 1-2-3 and very very powerful clunk, I though I would break my trans if I continue to drive a non0driavable car ! I parked the car for a month, removed battery for 3-day...no fix.

I read this FIX, I have not tried it so far, however I read another FIX saying you have to put the Car in tiptronic mode and shift at redline all 5 shift if possible and then come to complete stop without barkes to reset the trans. I took my Car out at 3:00 a.m and tried this 3-4 times but I could not get from 1-2 good but from 2-5 I would take off like a rock hitting 140M mph, GOOD NEWS it fixed my trans 2-5, however now I have a Bad 1-2, but my Car is basically drivable --- Please advise what else can be done ??

Leoric

Could you please tell us if the problem has returned. I am having the same problem and I am going to try this fix. Oh, and mines a 99 A6 2.8 Quattro.

Thanks!!!

Stampy

Back from the dead. Thank you archives. I did this a week ago and seems to have worked! Thanks MP