Diesel Injection - Fuel Injector Deviation Help - Engine Rough at Idle

-> My Car

Volkswagen Amarok 2011, 155k miles
4 cylinder Diesel 2.0 liter
Biturbo
Piezo electric injectors + CP4 high pressure pump

-> The Problem

Engine is running little rough at Idle. The issue is intermittent. On higher RPM I don´t see any problem. Issue only at idle.

When that happens I see RPM jumping between from 830 to 880 rpm. Engine kind of shakes a little bit.

Analyzing injector deviation values: The first injector is at +3.00 mg/str and second -1.0, while the rest seem to be around 0.50.

Issue tends to normalize when I drive at 2000 rpm, all injectors seem to be around or less than 0.25 mg/str.

Rail pressure its very close to expected value, but moving up and down all time.

When engine is running smooth measurement values at idle are less than 0.50 on all injectors.

-> What I have done so far.

I have replaced the Rail pressure Regulator and pressure sensor, cleaned common rail and pipes.

Did not seem to help.

-> YOur help is greatly appreciated

Should I replace injector #1? CP4 flow regulator ? look for leaks ?

Anything is greatly appreciated.

Many thanks