I've been chasing this p0505 code for awhile and other codes. It's the only one left. Compression and leakdown was fine. Deleted air pump and replaced with new IACV from honda (idle relearn). Did spray method with brake cleaner... apparently no vacuum leak. The only thing that I've finally notice are the pipes running under the car... vent, return, and feed. Two of the pipe are rusted but would any of those pipes cause p0505 code?

 

Have you double checked every single vac line in and around the IM?

 

Sorry for late reply. No vacuum leak but I adjusted the screw for my idle down to 900-1k rpm. It usually idle at 1200...no more p0505...