Willy337

Yesterday driving back the car suddenly starting running lumpy and was shaking me about, didn't feel smooth. It felt and sounding like it was misfiring. I got it connected upto VCDS Lite today and noticed that the lambda reading was showing -4.7% in the measuring blocks.

How do it fault find from here? Anybody got any suggestions?

silverd2

02 sensors do NOT cause misfires...the front sensors only make minor fuel trim adjustments within a preset "map", AFTER the MAF has made the major main fuel/air mixture adjustment. The rear 02 sensors do nothing, except to report performance of front sensors and trip codes when called for.

Look elsewhere for your problem...if it was misfiring, the CEL would be flashing and VCDS would read misfire code(s).
One (of several) possibilities: A failing torque converter clutch, can mimic a misfire feel, especially at medium speed at light throttle.

JoePGT5S

I agree with Sam. If this was engine related you'd most likely have triggered some codes. This may be the dreaded "shudder" that indicates a transmission issue. I had this just a few hundred miles before my transmission failed. I hope this isn't the case for you.

Willy337

The weird thing is I can feel it running lumpy when it's in park so presumably this wouldn't be gearbox. I totally hope not as had to wait a year to find a suitable dinar gearbox which got serviced and fitted about 2 months ago. At least I don't have to worry about 02 sensors then. Right back to basics I'll check the plugs and see if they're ok. Could do with a change anyway. I'll see what I find. Thanks for the info. Really appreciate your help guys.

2001 S8

[QUOTE=One (of several) possibilities: A failing torque converter clutch, can mimic a misfire feel, especially at medium speed at light throttle.[/QUOTE]

Could the torque converter shuttering be a software issue? The reason I ask is I had a 2001 Olds Alero and had a torque converter that was shuttering. I took it to a GM dealer and there was a bulletin that the torque converter needed a software update. After the update the issues was gone.

I know the Alero and A8/S8 are different animals but could it be something as simple as a software update?