Public innovation intermediaries strive to play a key role in translating participatory ideals into urban innovation practice. This article examines how such intermediaries shape community participation within open innovation projects, focusing on Forum Virium Helsinki (FVH), an actor in Helsinki's smart city ecosystem. Drawing on participatory urban planning and public innovation intermediation, the study assesses whether community participation yields meaningful co-creation or remains largely procedural. The analysis draws on FVH's project library (199 projects), from which seven were selected for in-depth qualitative study, combining document analysis with ten stakeholder interviews. A process-oriented framework compares engagement practices across project stages. Findings show a recurring pattern: while ideation and implementation feature visible engagement - surveys, workshops and test-user activities - participation during design and evaluation is limited and often symbolic. This reveals a gap between the rhetoric of co-creation and its practical realization. The study concludes that intermediaries like FVH both enable and constrain participatory governance. Although they facilitate experimentation and collaboration, institutional and project-based constraints restrict transformative participation. Embedding participatory innovation in ongoing governance is essential for inclusive, sustained community engagement.