260z reads discharging at idle
 

My 260z ampmeter reads discharge at idle and jumps up momentarily when engine is throttled. Is this normal because i just replaced the alt and voltage reg 2 weeks ago and it was reading like 40 amps at cruising speed. Slowly the amps have dropped over a week and now it discharges a bit at idle. Could it be the reg needs adjustment as I have seen in the service manual?