Anyone else having trouble with this? I can sweep pick to a standard level, but as soon as i turn the metronome on i fall to pieces. I find metronoming them slower is harder too.
How long have you been practicing sweeps? Also, how many notes are in each sweep? Try grouping them differently. Make sure you are saying the rhythms: TRI-PU-LET, TRI-PU-LET, or 1-e-and-uh 2-e-and-uh.

EDIT: Make sure you practice at slower tempos, it helps you gain control, and in turn, you become more fluid with motion.