S8 D2 erratic gearbox
 

hi everyone, have a few issues with my gearbox im trying to figure out

i have searched and searched for an answer so apologies if this has been covered before

the only similar thing i found was a thread by hpsauce who said he sold the car before rectifying the issue (thanks for the reply)

i've got a 97 S8, AHC engine, DYM gearbox, TCU code ends in BG

had it a couple of years but its started misbehaving, its not all the time and there seems no rhyme or reason to it, its just bloody annoying

if i got into a tight corner, when i try to accelerate away the car shudders for a couple of secs, as if a clutch is slipping, because its in 3rd and should be in 2nd, jab the throttle or wait for the shudder to end and it then drops into 2nd and away you go.

and then sometimes when i slow down in a straight line the gear change is erratic, usually 4-3rd or 3-2nd, the change down feels like i have jabbed the brakes for a split second

these things dont happen all the time so cant work out if the gearbox is goosed or the gearbox tcu could be the culprit?

the car throws up no fault codes and ive checked quite a few times

in tiptronic mode the car drives spot on, no slippage or erratic changing
kick the arse off it in auto and it drives fine, but i cant be doing that all the time i'll end up in a ditch!

if anyone else has had this problem please let me know, in my mind its terminal gearbox so anything other than that would be a bonus

thanks in advance!

If it was the F125 switch it would show on VCDS - which you say shows no fault codes so it would seem (IMHO) to be more of a gearbox mechanical issue than anything upstream or downstream. I am sure that others with greater insight than mine will be along shortly but I hope that it doesnt turn out to be a terminal gearbox fault tho' +++

Change the MAF +++

(by way of explanation, the MAF can appear to be working fine but actually be operating at the extremes of plausible values. It doesn't throw a code because it is giving values, and the ECU can compensate with the feedback from the O2 sensors, but the MAF is critical for the ECU to feed the TCU engine load information. If its at the limit of plausible it can confuse the TCU leading to erratic shifting. Its also considerably cheaper to change the MAF as a first step than to pull the transmission out!)

It was just such an insight from (no surprise) MJ that I would have expected +++

I don't have vcds, just a basic code reader, but it's always worked in the past (10 b5 a4,s & a6s) I can't really warrant spending the money on a vcds kit for a 20year old car I don't really use but could there be certain fault codes that is only shown on this type of equipment?
Thanks

Thanks for the reply mikkijayne. I had read about the maf sensor but most of the time it is fine and if I thrash the arse off it it never plays up. I'm not a mechanic by any stretch of the imagination but is it possible the maf sensor is playing up if it's only a certain gear or rev range that misbehaves? Are they that sensitive? Thanks

Yes!

My car has changed considerably since installing the new MAF. Gearbox behaviour especially, smoother, more intuitive, selects higher gears sooner than it used to on light throttle etc etc etc...

Ok thanks I shall give that a try then! +++

Now I would disagree with that, VCDS is an essential and saves you money, probably even the first time you use it.
You really do need to read the codes from the gearbox, does your code reader do that?

I'd start off by buying a cheap eBay generic cable and running VCDS-Lite in free/demo mode with it, that should enable you to see enough to check whether the gearbox itself thinks it's OK.
(You won't be able to reset errors or do full scans, but right now you don't need that)

Or you might find someone selling an old VAG-COM system, that would be all you need for a car of that vintage.

Where are you, there may be someone near you with VCDS that can scan for you?

If you dont want the expense of vdcs then go for the obdeleven dongle. I bought one for the s8 and it has been a godsend. Even managed to do my first bit of coding last week successfully.