Agree. Below the 3 bar level and the point where the pressure relief valve opens, any variation in engine speed is going to cause a variation on oil pressure.
Lack of idle smoothness is somewhat inherent to continuous flow fuel injection systems, and any variation in injector flow rate is going to make a cylinder run a little lean or a little rich, which is also going to affect emissions.
If everything else checks out - ignition, idle stabilization system, and basic mixture setting as indicated by the duty cycle, then the injectors are suspect. They can be cleaned and flow tested and should not have no more than a maximum of 3 percent variance from the highest to lowest.
They can also be replaced, but if there is evidence of loose dirt or other particles in the injectors, the entire fuel system should be flushed to attempt to remove any foreign matter that could wear new injectors and upset their flow calibration.
If the injectors including the shrouds have deposit buildup an Italian tuneup with a big dose of Techron in the fuel might help.