06/17/2026
Direct injection engines utilize fuel systems that enhance fuel efficiency, but cause carbon deposits to accumulate on the rear surfaces of intake valves due to the lack of self-cleaning fuel spray. This condition requires removal of the intake manifold and walnut blasting of the intake valves' rear surfaces. Common issues include rough idling, poor performance, stumbling, and in extreme cases, a check engine light. Subaru models 2020 and later are equipped with direct injection engines. This is on 54k mileage