I've had the same issue for 2+ years lol. I just haven't really tried to tear it down to find out. I would like to know what could be causing it though. For me everything on the steering wheel works fine so I don't think it's the clock spring connections. It could be my clutch switch but you have an AT so there might be some drive position sensor.
AUTOMATIC SPEED CONTROL DEVICE (ASCD) details are on the field service manual EC page 62.
Their is a surprising amount of systems and sensors involved with just maintaining speed.
Nissan 370Z Owners Manual / Service Manuals - Nissan 370Z Forum
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