The fuel pressure rapidly fluctuates, especially at idle:

The fuel pressure sensor is too close to the fuel rail. The VaporWorx system can react fast enough to chase
individual injector pulses at idle, hence causing rapid fuel pressure gauge readings. Once engine speeds increase
this tendency reduces. Move the fuel pressure to as close to the fuel module as practical. In some case where a
very short primary fuel line is used, a longer line from a “T” may be needed to install the fuel pressure sensor into.
This extra head length acts a damping system for the injector pulses. A Radium pressure damper has also shown
to be very effective.