In order to do the hpfp swap, you have to have a protune for it. Not only is there an issue with idle, it won't operate at the correct pressure to gain the benefits. Those who tried to run it with Maestro actually lost pressure and were worse off. The ecu is programmed to run the Bosch pump at a certain pressure and volume. The signal on the Hitachi pump from the VCV is all off for what the ecu wants to read and then communication with the lpfp will be all off as well. I ran it and logged it. My pressures were no different without a tune. Cold start is EPC and limp mode. Warm start and the pressure at idle fluctuates like crazy. I am going to be putting one back in tomorrow though and I have a custom file from Reflect Tuning to run it.
Injectors aren't as weak as the hpfp apparently. Just the factory cycle on them is barely opening them. Once tuned it becomes apparent. On the APR 100 octane is20 file, the hpfp is operating at 95%.