You are right to say that loss of residual fuel pressure will cause a hard-to-start situation. Once the engine has been turned off, residual pressure should not drop to under 1 bar (100kpa) after 20 mins. If you can see the pressure dropping rapidly then you have a problem somewhere.
With the loss of residual pressure, fuel vaporisation can occur in the fuel lines, which will cause hot-start issues. When the vapor has been given time to disperse (usually long enough for a cold start), the engine will fire up again.
A few components can contribute to loss of pressure:
- fuel pump check valve
- fuel rail regulator
- external leaks from hoses, fuel filter etc
A good way to test this is to hook up a fuel pressure gauge, run the engine, turn it off and then clamp the return line. If the pressure holds, you have a faulty regulator.
If the pressure does not hold, get another clamp and clamp the supply line. If the pressure holds, you have a faulty fuel pump check valve (which should not be the case if you have had a new Bosch unit!).
If the pressure still does not hold, you have faulty/leaking injectors and will have to get them checked/flow tested and serviced.
Fault codes can be checked by any good auto workshop, it is not necessary to go to Toyota. Fix up your loss of residual fuel pressure first and see if that helps your fuel consumption.
Hope this helps shed some light!