I have a 91 civic HB with a semi stock 1.5 motor. It only has a cat back exhaust setup, mild though- not over large. The auto shop checked everything they can think of including - injectors, plug wires, plugs, cap & rotor, cam timimg, compression, all sensors, coolant sensor, valve adjustments and throttle body. Everthing is OK @ 819 rpm - But high idle 2492 rpm it fails ---The HC's are 269 (limit 140) CO"s is OK .33 (limit 1.00)
I heard that high HC's are ignition related and high CO's are fuel related. The tech say's that there is a miss at high idle, but he can find it. Any HELP would be apprciated. California Chuck

 

most HC fails are very likely to involve an old and clogged PCV valve

 

Thanks Fast88std, I'll try a new PVC valve this weekend. See if it makes a differance. Chuck

 

Thanks again Fast88std, it looks like you where right. Removed the PVC valve and it was plugged. Put in a new $2.99 valve and the pusation at 2000 rpm is gone. While I was at it, I added new rear brake pads and new KYB rear coil overs. Time to ride. Chuck