I have a 91 civic dx 1.5 Its got a new cap, rotor,spark plugs, air filter, cat is about a year old.

First test
40km/h
HC Limit 86 result 91
co% Limit .048 result .40
NO 993 RESULT 147

idle
HC limit 200 reading 200
CO% Limit 1 reading 0.47

then changed the o2 sensor and car ran worse
40km/h

HC Limit 88 reading 137
Co% L 0.48 R 0.46
no L 993 R 822

Idle
HC Limit 200 Reading 245
CO% L 1 R 0.66

Also during both test the ignition was retarted as far as possible and I was running 93 octane gas. Should I run lower octane gas? Why would a new o2 sensor make it worse? Should I put the old one back on? Would running hotter or colder plugs help?

OK I'm a complete moron I just realized I didn't retard the timming i advanced it I'll try it again with timming actually retarted this time.
All and any advice is welcome.

 

lower octane gas burns cleaner...

you might want to run some seamfoam(nappa auto parts) through your engine to clean out those nasty carbon deposites... change your oil run a tank of gas and go back. run 87 octane or 89 whatever it is..

 

ok i highly recommand you go to kargen get the emission pass formula thing put into your gas tank it help for sure. i put in my it drop from 204 130-160 HC ok oh one more thing check your CAT maybe need to replace(try to borrow someone cat put it on see what up). that is what happen to me. my friend help me setup my ignition time about 15 degree something like the manual said is 16 is normal again i recommand you put that emission formula to your gastank and use gas treament and oil treament try to clean your car

 

Thanks I changed the oil about two weeks ago though. I'll try the lower octane with the timeing backeded of a little. One more question though Why would it do worse with a new sensor besides the obvious that its defective