Rough Idle in Subaru R1 Signals Throttle Body Issues

Had a similar situation with my 2005 Subaru R2. The check engine light came on with rough idle problems. Initially thought it was the throttle body, but diagnostics revealed an issue with the idle air control valve and air intake system. The air valve had carbon buildup restricting proper air supply. The mechanic found a cracked vacuum hose connecting the pump to the air valve, causing inconsistent idle speed. The repair required cleaning the throttle body, replacing the faulty hose, and recalibrating the idle air control valve. This was a serious issue since improper air supply can damage engine components long-term. Left unaddressed, it could lead to increased fuel consumption and potential engine damage. The symptoms match your description, unstable idle and check engine warning. Recommend getting the air intake system checked, particularly the connections and idle air control valve. These components often need attention around 150000 km mark. The throttle body might need cleaning, but its unlikely the root cause based on the symptoms described. My R2 has run smoothly since the repair with no idle problems or warning lights.

Thanks for sharing that experience with the R2. My situation was indeed very similar and turned out to be related to manifold pressure issues. Got it checked and there was a vacuum leak causing the engine stalling. The mechanic found it during a smoke test. Would you mind sharing what the repair cost you? Also curious if youve had any other idle problems since the fix? Hoping for a long-term solution like you got.

After getting my R2 fixed, the idle problems completely disappeared. The total repair cost was 175€ for replacing the defective hose connection from the pump to the air valve. This fix proved to be a lasting solution, its been running smoothly for over a year now with no vacuum hoses issues or irregular idle speeds. The air valve repair definitely resolved all the symptoms. No more rough idling or check engine lights since then. The throttle body cleaning they did as part of the service probably helped too, though the main issue was clearly that faulty connection. Worth noting that proper maintenance of the air intake system after the repair has kept everything working well. Just a quick spray cleaner on the throttle body every oil change helps prevent buildup from reoccurring. Your manifold pressure issue sounds similar to what I dealt with, these vacuum-related problems often show similar symptoms.

Thanks for the advice. I took my R1 to a different mechanic this time who actually found multiple vacuum leaks during testing. The main issue was a cracked vacuum hose near the intake manifold, plus some deteriorated smaller hoses that needed replacement. The total repair came to 230€ including parts and labor. The mechanic also cleaned the throttle body and checked the idle air control valve while everything was apart. Been about 2 weeks now and the car idles perfectly, no more check engine light or rough running. Really glad I got a second opinion instead of just replacing the throttle body like the first shop suggested. The smoke test they did made it easy to spot exactly where the vacuum leaks were. Car feels like new again.