I replaced the master cylinder a servo on my mk4 escort yesterday,but now my brakes feel really spongy. Iv bled the brakes but still no joy(made sure rear wheels were on the ground to) I do have a afr gauge fitted and have noticed that when i press the brake pedal the car runs lean, but will return to normal when i lift off the pedal I have double checked everything is tight but im slightly confused now. Anyone shed some light?

cheers