forget about code 20 as long as your alternator is charging(aprox 14 volts).But you should look into code 12(egr).I'm assuming the H-22 is in a civic.There's one piece that usually gets overlooked when that swap is done.
The egr valve is on the motor,but the vaccum goes into a box where all the controls for the egr valve are.Since the civic does not have this box, You must aquire this box,open it up and extract the egr control solenoid valve,and hook it up as required.This part can be found on any 90-93 honda accord,and should cost not more than $50.00.Also in this box is the map sensor .Good luck.
P.S. code 20 will only show up when you ground your service check conector,it will never give you a CHECK ENGINE light.