Subaru Impreza Stalling: IAC Valve Repair Guide

Had the same stalling engine issue on my 2011 Subaru Legacy diesel. The symptoms were identical, unstable idle and engine stalling at stops. Initially thought it was the IAC valve too, but diagnosis revealed heavy carbon buildup in the intake manifold and throttle body. The engine stalling became more frequent until getting it properly checked was unavoidable. The throttle body required complete disassembly and professional cleaning. The intake manifold needed similar treatment due to excessive contamination. While servicing, they also replaced the air valve since it was partially seized from the carbon deposits. This is a known issue with direct injection diesel engines. The repair involved specialized cleaning equipment and recalibration of the idle control system. It was a serious job requiring around 6 hours of labor. DIY attempts can damage sensors and coating if wrong cleaning products are used. Would strongly recommend getting a second professional opinion, especially with those low kilometers. The stalling condition will likely worsen if left untreated, potentially leaving you stranded. Make sure they inspect both the IAC valve and check for intake contamination before starting repairs.

That repair sounds exactly like what my Impreza needed. The unusual stalling at idle speed was driving me crazy. Especially since it would die at the worst possible moments like traffic lights. Did you keep track of the total repair cost? Mine was fixed about 6 months ago and the throttle body cleaning plus IAC valve replacement ended up being pretty expensive. Just wondering how the prices compare and if you had any recurring engine idle issues since getting it sorted? The stalling completely stopped for me after the repair but Im still carefully monitoring the idle behavior just in case.

Thanks for asking about the costs. Getting my Legacy fixed 6 months ago was definitely worth the 425€ total for the thorough intake cleaning and bad idle air control valve replacement. Not a single engine stalling issue since the repair. The price included complete disassembly of the throttle body, professional cleaning of all the heavily contaminated intake components, and the new IAC valve. The stable engine idle made such a difference, no more sudden stalling at traffic stops. My mechanic showed me the old parts and the carbon buildup was shocking. The air intake system was seriously clogged. Now the idle control works perfectly and engine runs smoothly at all speeds. Regular throttle body cleaning is now part of my maintenance schedule to prevent future buildup. A stable idle is worth every cent spent on proper repairs rather than risking DIY attempts that could damage sensitive engine components.

Thanks for the advice. After seeing all the replies, I finally took my Impreza to a different mechanic last week. The engine idle problems were exactly what you described, heavy carbon deposits blocking the throttle body and a failing IAC valve. The repair bill came to 390€ which included a full cleaning of the air intake system and replacing the faulty air valve. The mechanic showed me the old parts and the carbon buildup was terrible. No wonder the engine kept stalling. Been driving for 5 days now and what a difference. The car holds a perfect idle, no more sudden stalling at traffic lights, and the check engine light is gone. Should have done this months ago instead of trying to live with the problem. Going to follow the advice about regular throttle body cleaning to prevent future issues. Definitely learned my lesson about not ignoring unstable idle symptoms.