Point 1.Actually i did cover the pipe, and i felt the change. Now the engine is shifting gears a little late, meaning more pick-up and power. Is that was is supposed to happen? IF yes, then good.
Point 2.About the RPM, even my car drives at 5-6km/h when just on D, but when i turn the AC on it falls down to 3-4km/h, Although the engine doesn't vibrate but you can feel as if you car slowed down. If you know what i mean. Does it have to do something with the idle setting or the CNG Peak screw at the top? Cos my idle screw is now 40-50% open, since you said opening the screw outside increases idle, right?
Point 3.Your car pic above, you spray diesal, but you wash your car, i got my car washed, the water sliped into plugs and god knows wherelse, completely ruined the pickup and drive with jerks and stuff, so my mechanic told me never to use water again for engine, and he sprayed something(Fluid like thing from his Pressurised GAS Pipe) he said it's a mixture of oil,atf etc which cleaned the engine but didnt' screw the plugs n stuff ( SO yeah a tip of advice for you here :D)