ok.... This is my first time posting on this site so to start...... Nice meeting you thanks in advance for any help!

I have a 99 Civic SI, upgrades to engine, Cat back Greddy, Cold Air Intake, Fuel Pressure Reg.
Just put new plugs and wires on it and always run premium octane

Problems....
1. My air/ fuel ratio gauge has a rythmic jump to it.... as in it jumps from the most "lean" to just before "Ideal" unless I'm giving it half throttle or more. It never does it if I'm at 4800-5000 rpm or more...When I hit those RPMs and it stops jumping, it gets MUCH more power. Even under light throttle.... I know its not the VTECH doing it cause it hasnt engaged yet...not till late 5000's. My mechanic set the pressure and i'm wondering what spec is so I make sure its not wrong and killing my engine...
2. Tonight my check engine light comes on and starts BLINKING....then steady. Obviously scares me to death... I THINK the codes are, system to rich bank 1..... and something about a sensor. I cant find any code list that says its for my engine so I'm not sure the others.... and I dont know how to reset the ECU to see if it throws them again... I tried the fuse pull and didnt have any luck.....

Thanks again, John