RS4 Engine Light and Rough Idle Points to Air System

As an RS5 (2011) owner, I encountered nearly identical symptoms. The rough running combined with check engine light pointed to a vacuum leak where the brake booster hose connects to the intake manifold. This created an unmetered air supply issue affecting engine performance. The vacuum hoses in these V8 engines often develop tiny cracks near connection points due to heat cycling. When checking the system, focus on the hoses running between the throttle body and brake booster, these are common failure points. A smoke test revealed multiple small leaks in my case. The repair required replacing several vacuum hoses and recalibrating the throttle body position sensor. While not a major mechanical issue, leaving vacuum leaks unaddressed can lead to poor fuel economy and potential damage to other components. Quick checks you can perform: Listen for hissing sounds around the intake manifold, Inspect all visible vacuum hoses for cracks, Check if brake pedal feels harder than normal, Monitor if idle smooths out when throttle body is cleaned These symptoms deserve prompt attention but dont indicate serious engine damage if addressed soon.

Thanks for sharing that detailed experience. Had very similar idle problems with my 2008 RS4 last year, and your vacuum leak diagnosis matches what I found. The engine stalling and rough running turned out to be caused by deteriorated vacuum lines affecting the manifold pressure readings. Did you remember roughly how much the repair cost in the end? Also curious if youve had any recurring air intake issues since getting it fixed? My car has been running smoothly after the repair, but Im keeping an eye on the throttle body since thats another common failure point on these engines.

Had the work done last week actually. The mechanic found a faulty hose connection from the pump to the air valve, which was causing inconsistent manifold pressure readings. Total cost was 175 Euro for parts and labor, not too bad considering the symptoms. Since fixing that vacuum leak, the engine runs perfectly smooth with no air intake issues. The rough idle and stalling problems disappeared completely. Regular inspection of vacuum hoses is now part of my maintenance routine to catch any potential issues early. These V8 engines are sensitive to proper air supply, so keeping the intake system sealed is crucial for optimal performance. The throttle body is worth monitoring as you mentioned, but often the simpler vacuum hose connections are the real culprits. My advice would be to have a thorough check of all vacuum lines if symptoms return, before assuming throttle body failure.

Just got back from the mechanic after dealing with those exact issues on my RS4. The symptoms matched perfectly, rough idle and check engine light came on around 121000km. After checking the vacuum hoses near the throttle body, they found multiple hairline cracks causing air leaks. Total repair came to 220 Euro, including new vacuum lines and labor. The mechanic showed me the deteriorated hoses and explained how the air supply getting past the air valve was throwing off all the readings. Makes sense why the engine was running so rough. Really glad I got it sorted quickly. The car runs perfectly smooth now, no more stalling or rough idle. Going to keep checking those vacuum hoses regularly during maintenance. These V8s clearly need proper attention to the air intake system to stay running right.