I've had this civic for about 2 months and am slowly discovering its issues as the cold weather sets in. Now that it's in the 30/20's °f it struggles to stay started on cold start and I have to gently give it gas til it figures its life out. All starts after are normal unless it sits long enough to get completely cold again. Also has intermittent P0505, only shows up after stopping at a light, bucks like crazy unless you really get into the accelerator until I can pullover and clear the code. Once code is cleared its fairly normal. I've noticed the colder its gotten the more frequently the code appears, followed by some hesitation after clearing. Previous owner "deleted" air assist valve with some jb weld, stuck a bolt in the corresponding hose in the intake hose and capped the nipple on the manifold. They also disconnected the breather hose, tried reconnecting and the car refused to start. The rpms do not surge when idling, throttle position sensor when idling is between 8.6-9%. Any recommendations before I start throwing money at this???

 

Check for vacuum leaks. Cover the port in the throttle body at idle. If engine speed drops its probably ok, if not you got vacuum leaks.

When warmed up and idling, disconnect the IAC connector. If engine speed doesn't change replace the IAC. If it does or stalls, adjust the base idle speed to spec