This is the AWM 20V Turbo engine so replace the coolant pump as it's driven by the timing belt and is best replaced as a preventive measure. The idler should rotate freely and after install adjusted per the bentley manual. Adjustment is tricky as the directions aren't very clear. Be careful and check the adjustment a few times as a jumped belt on this engine is a bad thing... I did not use thread locker on my AWM when I did the jo b, just followed torque requirements.