S8 Throttle Valve Issues Causing Power Loss and Rough Idle

As someone with some mechanical experience, I dealt with nearly identical symptoms on my 2004 A8. The throttle sensor was indeed failing, causing similar issues with engine idling and putting the car into limp mode occasionally. After noticing the response delay and rough idle, I took it to my regular workshop. They ran a full diagnostic which pointed to the accelerator pedal module. The electronics inside had degraded over time, a common issue with these models. The total replacement cost came to 265 Euro including parts and labor. The repair solved all the symptoms: Rough idling disappeared, Normal throttle response restored, Check engine light cleared, Power returned to normal, Consistent air flow resumed Before suggesting more specific advice, could you share: Current mileage on your S8? When did these symptoms first appear? Does the issue happen more when the engine is cold or warm? Have you noticed any other warning lights? These details would help confirm if your issue matches what I experienced with my A8.

Thanks for your response and helpful diagnostic experience. My S8 has 95928 KM and had its last major service 6 months ago. The symptoms first appeared about 2 weeks ago and seem worse when the engine is warm. The check engine light is the only warning light currently showing. The rough engine idling and response delay are particularly noticeable during highway merging, which really impacts fuel efficiency. Based on your similar experience, I will have the accelerator pedal module checked first. Good to know this could potentially fix both the air intake issues and power problems. The repair cost you mentioned seems reasonable compared to what I was expecting for a potential throttle body replacement. Would be interested in hearing if anyone else faced this specific issue and how long the repair lasted before any problems returned.

I can confirm the repair has held up perfectly on my A8 for the past year. Since the pedal module replacement, fuel efficiency returned to normal and I have not experienced any more issues with response delay or rough idling. The symptoms you describe match my experience exactly, especially the worse performance when warm and the problems during acceleration. The workshop mentioned that deteriorating pedal modules often show these exact patterns on our engine type. Quick tip from my repair experience: make sure they also check the wiring harness connecting to the pedal module while doing the replacement. In my case, there was some minor corrosion on the connectors that they cleaned up, which helped ensure a proper fix. The total repair cost seems consistent across these models, you should expect something close to the 265 Euro I paid. Much better than the 800 Euro+ a complete throttle body replacement would have cost. Mind updating the thread once you get it checked? It would help others to know if your fix ends up being the same as mine.

My S8 is all fixed now and wanted to close the loop on this thread. The workshop confirmed it was indeed the accelerator pedal module causing the issues, just as suggested here. The final repair cost was 280 Euro which included cleaning the connectors as recommended. Since the fix last week, all symptoms have completely resolved: No more check engine light, Normal throttle response is back, Engine idling is smooth again, Air flow is consistent, Full power restored The diagnostic process was quick since I could point them toward the pedal module based on the feedback here. They still ran a full check to confirm, but having this direction saved time and likely reduced costs. For anyone searching with similar symptoms later: the key indicators were rough engine idling, throttle response delay, and worse performance when warm. Getting the pedal module and connectors replaced/cleaned was a straightforward fix that cost far less than a full throttle body replacement. Thanks again for the help. Really glad I checked here before authorizing more extensive repairs.