Going back at another one of your post with the same complaint, I mentioned FP regulator on that post also, but you were inclined to think that the fuel pressure would not effect the idle and you notice no complaint at higher RPMs
Well, I will explain it to you and then leave it there.
The FP regulator is vacuum controlled. It's purpose is to keep the pressure from the fuel pumps at a pre-determined specification for the injectors , thru a fuel rail.
This is done with a vac actuated diphragm inside the regulator...BUT..what happens to these regulators is they get a leak in that diaphragm and that allows raw gas to get sucked into the engine thru the operating vac hose. So, you now have a supply of raw UNMETERED gas entering the intake of the engine,thru the regulators vac hose ..The results is erratic idle b/c this new gas supply is not sync into the fuel management as the Injectors are.
So, you may dismiss this fact, or you may want to see if gas is comming out the FP regulator port. It is not uncommon and ,as a matter of fact, it is standard procedure on your complaint.
One will not notice this fault at higher RPMs b/c the engine can then correct for this small amout of unmetered gas.
After doing all you have to correct the problem, I would take the 2 seconds time it take to check that regulator ...