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paulahuber6

RS3 Idle Issues Point to Faulty Air Control Valve

Check engine light on

My 2012 RS3 keeps throwing a check engine light and I suspect an air valve issue. Engine runs rough at idle and occasionally stalls when coming to a stop. The throttle body seems slow to respond and idle problems are most noticeable when the engine is warm. Already checked and cleaned the air supply components but the issue persists. Looking for input from others who had similar symptoms, what was the root cause and repair solution in your case? Any specific components I should have the workshop check first? Let me know your experiences with similar issues.

4 comment(s)


emilflame8

I had a very similar issue with my 2010 S3 last summer. Having some experience working on engines, I first tried the basic checks myself but eventually needed professional help. The symptoms matched exactly what you describe, engine stalling, rough idle, and sluggish throttle response. The main issue turned out to be a deteriorated vacuum hose connecting the brake booster pump to the intake manifold valve. The vacuum leak was causing unstable manifold pressure, particularly noticeable at idle. The workshop found the problem using smoke testing equipment. Total repair cost was 175 Euro, which included replacing the defective hose and rechecking all vacuum connections. Since the fix, the engine has been running smoothly with no more stalling or rough idle issues. Before suggesting more specific troubleshooting steps, could you share: Current mileage on your RS3? Any modifications to the intake system? Have you noticed any unusual sounds from the engine bay? Does the rough idle get worse with the AC running? These details would help determine if your case might be related to the same vacuum system components that caused my issues.

paulahuber6 (Author)

Had my last service at 150594 KM and they verified the manifold pressure sensor was working correctly. After seeing your symptoms and repair experience, it sounds remarkably similar. I agree a vacuum leak test would be smart since cleaning the throttle body and air components didnt solve my check engine issues. The engine stalling and rough idle symptoms match exactly, especially with a warmed up engine. Going to book a pressure test at the workshop and have them inspect all vacuum lines, particularly around the brake booster area you mentioned. Did your check engine light clear immediately after the repair, or did it take a few drive cycles?

emilflame8

Thanks for the follow-up. Yes, my check engine light cleared after about 3-4 drive cycles following the vacuum hose replacement. The workshop explained this is normal since the engine control unit needs to verify stable manifold pressure readings across different operating conditions before resetting the fault code. Since your mileage is similar to what mine was when the issue occurred, those vacuum lines are likely at the age where deterioration becomes common. The air supply system on these engines is quite sensitive to even small vacuum leaks, which explains why the idle problems get worse as the engine warms up and the rubber components expand. One tip before your workshop visit, make sure they check all the small vacuum lines running to the manifold pressure sensors too. In my case, the main brake booster line was clearly cracked, but they found a second smaller line that was also starting to fail during the smoke test. Getting both replaced at once saved me from having the check engine light return a few months later. The good news is that once all vacuum-related components are properly sealed, these engines typically return to a perfectly smooth idle. The manifold pressure stabilizes and the air intake system can maintain proper fuel mixture control.

paulahuber6 (Author)

Thanks for passing along that information about your repair experience. The light usually takes a few drive cycles to clear after vacuum system repairs, so that matches what I should expect. My car has no intake modifications and the engine sounds normal other than a slight surging at idle. AC does make the idle problems worse though, so Im convinced its likely a vacuum leak causing my air supply issues. The throttle response issues and engine stalling match the symptoms you described perfectly. Going to schedule the smoke test and have them do a thorough check of all the vacuum lines, especially around the brake booster and manifold pressure sensor connections you mentioned. Better to replace any questionable hoses while theyre already checking the system. Really hoping this resolves the rough idle and check engine light for good. Will update once I get the results back from the workshop. Thanks again for sharing your experience, it helped point me in the right direction for diagnosis.

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