I have a 1993 Toyota Pickup, 22RE I4 engine with EFI. 300Km... Good compression,no oil burning, 5 speed manual.
FAILED HC Test limit 66ppm reading 209... PASSED HC Curb Idle Test limit 200/ 129
FAILED CO% limit 0.37 reading 8.34... PASSED CO% Curb idle limit1.00/0.18
PASSED NO limit 968 reading 36... N/A
RPM @ 2525... RPM @ 867
Dilution 17.4... 10.3
These results seem to indicate a very rich mixture at higher RPMs. Prior to testing I did a complete tune up including new NGK Iridium plugs (correctly gapped), wires, distributor cap and rotor, PCV valve, air and fuel filters. I set the timing to specs (with Dianogtic terminals jumped). I changed the oil (synthetic) and filter. The exhaust system was shot, so I replaced the Cat and muffler with new Magna Flow low restriction (2 1/2") parts. I reused the original front pipe with the O2 sensor in it... a header and new induction system will follow when I have $$$$. I did not adjust the valves as they are not noisey.
Since the test I have tested everything I can think of that would give high HCs and COs.
This truck uses an Air Suction system (Passive/Pulse air system, not an air pump)... it is working properly.
I've tested the Coolant Temperature Sensor both in the truck and on the bench... it's OK.
I've tested the vacuum switching valve for the high temperature line pressure up system... OK.
The fuel pressure regulator seems to be working properly, but I don't have a gauge..
The Dash Pot filter is clean and it works OK.
There are no codes stored in the ECM. It is not an OBD-II system.
When I tested the O2 Sensor initially (after warm up) I was getting readings of 150-200mV @ idle, 800-900mV @ 2500 RPMs. Later it jumped to 500-600mV & 900-1400mV..
My Haynes Emissions Manual says to watch for a voltage drop when you disconnect a vacuum line(too lean).. it did, and a voltage increase when propane is added through a vacuum line(too rich).. it did.
Do you think the O2 Sensor ($200) is Boffed?. or is the ECM not adjusting the fuel mixture?. or could the Magna Flow Cat be at fault?. too low back pressure maybe?
HELP! John.

So, you truck failed the emission test and you can't get you plate stickers. Now you have to have repairs done and a new emission test if you want to drive it. I don't see the point of your question.

. Add Shell Regane or Chevron Techron to the tank, in order to clean throttle body, valves, and pistons. This can definitely help lower emissions.
. Replace oxygen sensor. 300 km is an awful long time for an oxygen sensor to keep working properly.
. Consider replacing Iridium plugs with the same plug brand and number that came in the truck.
. It's hard to believe you can't test for codes.
. Did you set idle rpm to specs, before checking timing?

Put a new o2 sensor in it. They're only good for 80,000 miles. Period!

HC is normally caused by unburned fuel. If it misses a little it will raise HC. HC is the rich indicator and CO is the lean indicator. Normally both don't show up failing together unless the cat is bad. You may have the wrong cat installed(Not enough catalyst) for your application. In the states, you can't replace a California cat with a federal for the same reason.