08 MS3 running lean at idle, hpfp pressure low at idle when warm

so i just rebuilt my 08 speed3 with manley rods and pistons all factory sizing, as well as a overhaul gasket kit and a ACT clutch and light weight flywheel, was working on the break in and got about 15 miles on the car after verifying that all was running good with no leaks, and while sitting at a stop light engine rpm dropped to around 500 RPMS and with a rough idle as well as a CEL with a lean at idle code. preformed a data log while idling to view readings, and while idling the hpfp reading is around 90psi. when i give it some throttle the reading jump to around 1200psi which is what i assume is normal, then when it returns to idle it drops back down to around 90 psi. any ideas as to what this could be? pretty sure its something with the hpfp, just not sure if it sounds like the pump itself or if its the PRV. i will be doing the PRV test today just to see. no mods to the hpfp, only mods on the vehicle are the internals, cold air intake, exaust, and the accessport (which i just got after the rebuild)

 

Sounds like prv

Do test to confirm

 

did the PRV test, and it failed pretty bad, got to around 1500psi before dropping off. when it started dropping it was also very slow to do so is this pretty common for it to drop slow or should it drop instantly?