D2 S8 revving up and down while driving between 1000-2000 revs!!!!

[soldendave]

Hi guys

was wondering if you will give me some advice, i recently bought a 51 plate S8 D2 with 89000 miles on the clock which i absolutely love to bits. I checked as best i could that the gearbox/transmission was good at the time i bought it but recently it has started to revv up and down when driving in any gear at a constant speed beween 1100 and 2000 revs.

The rev needle bounces just slightly revving from 1200-1400 and back down etc as an example. this will happen maybe 4-5 times then it will go away only to come back later.

I am hoping that the gearbox is not on it's way out

From what i can find out from reading the threads here and on other forums it looks like a transmission flush may be a temporary fix. as the torque converter may be clogged up.

I am guessing a bit here and would be greatful for your thoughts. Does anyone know where i can get this done? how much it would cost? What is likely to be the problem?

Thanks in advance

Dave

[pcm2048]

I have a 2002 S8 with the same symptoms. On a trailing throttle it will gently surge between 1300 and 1400 rpm when travelling between 40 and 60 kph. It never happens when the car is cold or temperatures are mild. It will consistently happen on hot days and gets worse on very hot days. It is rarely noticeable as you must be on a trailing throttle. I have had the car for 18 months and it had travelled 80,000km at the time and has now clocked up 105,000 km.

When it first happened I got the transmission oil changed which made no difference, although the changes got slightly smoother, but they were good to start with so this was minimal improvement. Like you, I looked for some help but found nothing. The best I could establish was that it is a common problem. Some people said they had had the transmission overhauled and it made no difference.
As I have now travelled 25,000 km and it has not got worse, and it rarely happens, I am just living with it as it is a very minor issue.

I subsequently did some more research and the best indication I have managed to track down is that it might be related to a faulty O2 sensor. This does seem to make sense as the way O2 sensors work it might be giving a faulty signal to the injection which causes the slight surge. A number of people have said they have changed sensors and the problem went away. My difficulty was that the car has 4 O2 sensors and I didn’t feel like paying for and replacing 4 sensors when the problem is so minor.

I suspect you can ease your mind on the transmission based on my experiences and what I have read from others. If you do decide to replace the O2 sensors would love to hear if it works. Ideally it would be preferable to track down if it is only one and replace just that, but have not found any suggestions on how to do that given the faulty is so minor and intermittent.

[jonah290]

Hi,
You could try having the person that does your servicing, put the computer on it and reset the throttle body. This solved it on mine but only on tick over.

Regards
mark

[soldendave]

Well I'm not any further forward yet just learning to live with it for now. Only thing is that the car wouldn't start for about 5 turns of the key. It would turn over fire up and then immediately cut out. Did this 5 times in a row then started fine after that. Is thi a sign of something to come??? :-s