Q8 Diesel Stalling: Bad Idle Control Valve Symptoms

The idle symptoms match what I experienced with my 2018 Q7 3.0 TDI. The rough idle and stalling pointed to a severely contaminated air intake system and throttle body. The IAC valve was completely clogged with carbon deposits, which caused erratic idle control. The repair involved a thorough cleaning of the entire air intake tract, throttle body, and IAC valve assembly. This was not a quick fix, the technician had to remove multiple components to access and properly clean the system. In my case, the throttle body also needed replacement due to internal damage from the contamination. These idle control issues can lead to more serious problems if left unaddressed. Carbon buildup affects engine performance, fuel economy, and can damage other components. The check engine light typically indicates the ECU is detecting irregular air-fuel mixtures due to restricted airflow. Based on your mileage, this could be premature contamination possibly caused by short trip driving patterns or fuel quality issues. Would recommend having a certified technician perform a full diagnostic, as simply cleaning the components might not resolve underlying causes.

Thanks for sharing your experience with the Q7. I had the exact same problem with my Audi Q8 earlier this year. The engine stalling became so frequent that I barely made it to the service center. The idle speed was all over the place and the engine would just die at traffic lights. My dealer found similar issues with carbon deposits in the throttle body and had to do a complete cleaning of the intake system. The engine stalling completely stopped after the repair. Do you remember the total cost for your repair? Was the throttle body replacement covered under warranty? Also wondering if youve had any recurring idle control problems since the fix?

Glad to update on my Q7 situation. Since having the IAC valve and intake system serviced, the engine idle has been perfect with zero stalling issues. The rough idle problems completely disappeared after the thorough cleaning of the contaminated components. The total repair came to 425 Euro which covered the extensive intake system cleaning and IAC valve service. Unfortunately, the throttle body replacement wasnt covered under warranty since the damage was attributed to carbon buildup rather than a manufacturing defect. The investment was worth it though, the engine idle is now consistently smooth and I havent experienced any idle control problems in the months since the repair. The stalling engine issues that used to plague me at every stop light are completely gone. Just make sure your mechanic thoroughly cleans all components of the intake system when doing this repair. A partial cleaning often leads to the problems returning much sooner.

After getting advice here, I decided to take my Q8 to a different certified service center. The car idle was so unstable I had to get it towed there. They found heavy carbon deposits affecting the IAC valve and intake system, just as others described. The mechanic did a complete cleaning of the air intake components and tested the idle control system. The entire job cost 380 Euro and took about 4 hours. They showed me the cleaned parts, the amount of carbon buildup was shocking for such a new car. The engine stalling issues are now completely fixed. The idle speed stays perfectly stable and the check engine light is gone. The new shop did great work and I will definitely return there for future services instead of my previous mechanic. For anyone else facing similar problems, dont wait too long to address rough idle symptoms. The carbon deposits can cause more expensive damage if left unchecked. Getting a proper diagnosis and thorough cleaning of the intake system was the right solution in my case.