Low prssure at low rpm in 912 is

I would check the voltage at the fuel pumps next.

With the 912is engine the fuel pressure regulator operates with respect to manifold pressure (MAP).  So your fuel pressure gauge needs to either reference the air box pressure or be corrected for this on your display.  When your engine is off with the pumps running, manifold pressure equals outside air pressure so the gauge is accurate.  

When the engine is running at idle, the MAP is much lower than outside pressure so the gauge is going to read low. When you increase rpm the MAP increases and the gauge reads closer to what the regulator is asking for based on MAP.  At WOT your MAP is once again very close to outside air pressure so the gauge is very close to correct.  

There are fuel pressure senders that allow you to connect the reference source to the air box, which will then give the correct reading. Also, most electronic displays will have a setting that lets you use a standard sensor and correct for MAP.

This has been discussed here before, and there have been some threads that discuss setting up your flight display correctly.  Check out this thread for G3X setup discussion:

https://www.rotax-owner.com/en/912is-technical-questions/7997-setting-fuel-pressure-on-garmin-g3x

And here is a similar discussion regarding the Dynon setup:

https://www.rotax-owner.com/en/912is-technical-questions/8767-fuel-pressure-issues-low