What you do is use your metronome to focus on timing and accuracy.

Start by setting your metronome to around 40bpm. Playing one note to every click, exactly on the beat, try and sweep through the arpeggio, making sure every motion is perfect (if it's not, play slower) and every note is clear - with no unintentional notes.

The metronome is there to keep you locked in to the timing and focused, but it's the perfection and attention to detail of your practice that's important.