My 2005 Audi S4 Cabriolet 4.2 liter V8 has been a great ride for the past 73,000 miles. Only one problem. for the past year when I come off the highway and stop at a light within a minute or so the engine begins running ruff like its going to stall and the engine light blinks. I've taken it to Audi and the computer shows the light but they have no solution. Audi recalled the coils so I had them all replaced. It still has the same problem. The Audi service manager says its dirty so I've been running Lucas gas additive in it for months as well as their once in every 3500 mile cleaner and to no avail. I know I have a timing belt scheduled service replacement due at 75,000 but folks have told me that this couldn't be the problem. I hope someone out there might have a clue. I really love this car and want it to run right. Thanks for any advice you can offer.
There are two service bulletins on an engine misfire.
The first one is 240872. It states that the intake manifold bolts can come loose causing an engine misfire when hot. The fix would be to tighten the bolts and if it doesn't help then to replace the intake manifold gaskets.
The second service bulletin is 240850. It states that the ECM needs reprogramming because of the improper operation of the Intake Camshaft Adjuster Valves. This condition may or may not be for your car because it is for a misfire when the car is started when hot and a misfire occurs. It would be worth looking into for the engine misfire because the Intake Camshaft Adjuster Valves are adjusting when you are decelerating from highway speed to a stop.
The Timing belt is very important and should be done on schedule.
These are the common ones I found. Hope they help. Let us know how you make out.
2004 S4: I also have same issue. Misfires at idle after a 30 min drive or so. Took it to the dealer. They tried everything and now they are saying they need to check the cam valve adjustment. They believe the timing on one bank is not correct. However, for just diagnosing it, it would cause 3600 USD. Since you also have seen similar issue, was wondering if this proposed fix (diagnosing and replacing the CAM chain) makes sense. Thanks!
$3600 seems high for diagnosis. Replacing the timing chains should be more in the $2500 range.
I don't see any technical service bulletins about mechanical failures of the chains or variable valve timing components -- just the software update. But I have seen chains stretching and setting codes. Usually due to the cam and cranks position sensors getting out of sync due to the stretch.
No techs know your car better than the guys at the Audi service department. Let's just hope if there not sure about the problem, they have consulted with Audi tech-support.
We have just experienced the same fault in an a4 and we came to the diagnosis of a clogged cat. converter on that side . To diagnose the same in yours simply remove the upstream o2 sensor , leaving the electrical connector plugged in and crank again to see if symptoms are gone . He had installed new plugs , coils , wiring harness , intake seals etc. etc.
Hope this helps the next guy in a jam.
Yes, I used to have similar problem as you are seeing now. And I was given the same recommendation to check the cam timing. However, when I was ready to do that, winter came and the issue stopped showing up. Issue generally comes up in the summer when the ambient temp is high. So I did not want to check it then because I would not be sure if it is really fixed or not. However, this summer the issue is not showing, for whatever reason. Lately, it is showing up very few times but not that severe. And at the same time, now it is winter again. So I guess I will wait until Summer again. Sorry, for not able to help you now. But do let me know what you find in case you get it checked.