Ideally you want within around 0.5 volt of the battery voltage, was the earth new on the pump as well ?, the voltage should be the same under full load, this can be easily watched for on the rollers, the only thing that will increase under full load will be the amps used by the pump, this will if you have a bad connection/joint etc cause a major volt drop, but not if all is good wiring connection/joint wise.
Your idling may just be a dicky iscv, but something is telling it to raise to that amount, normally on the std ecu's it's the TPS reading.
For some reason these bosch pumps don't seem to like any time idle, mine was perfect when laid up for engine build, but decided it had enough, and surged like buggery up and down pressure wise, not very impressive at all for what is a expensive pump, if, or rather when it goes again it certainly won't be a bosch one going back on there, I'll be running twin walbro's, work out same price but hopefully better quality/longevity.
Mine was 2 years old, no debris problem, tank is brand new as is filler and all pipes.
I check the fuel pressure is not fluctuating, and if not within say a year old replace fuel filter, before having it set up/rollered I'd replace the CTS also.