It's a challenge to tune the PI loop. It can lead to very severe and wild behavior. To get snappier throttle, it's probably better to adjust t-pwm-gain and t-pos-gain. But if you must, I would start ki at 0, and gradually increase kp until "overshoot is observed", and then back off a bit on kp, and then gradually increase ki until the convergence is nice and fast, but no overshoot.
Check out post 239!
http://forums.24hoursoflemons.com/vi...p?id=8920&p=10