When your car is misfiring/running horribly, the engine vacuum will be extremely low. That is why the brake pedal feels stiff. You don't have engine vacuum to assist in braking. I'm still going with a sticking oil control valve for the VVTi. If the intake cam stays in the advanced position it will run fine over about 2000 RPMs, but at idle it will sputter, misfire, and generally run like a bag full of buttholes. You can try cleaning the valve, but I've never had any luck with that as a permanent fix.