Po221 - throttle pedal sensor position circuit fault (car will start with this code)
Po100 - air flow meter/MAF fault (car will start with this code)
Po1000 - this is normally shown if codes have been deleted previously and OBD drive cycle not carried out (does not effect running of car)
P1211 - Injector Control Pressure Sensor Above/Below Desired Level.
P2291 - fuel pressure low on cranking
P0251 is due to lack of fuel pressure, can be pump failure, can be injectors leaking back excess fuel which reduces pressure - ideally needs leak off test doing on injectors and fuel pressure test on live data.

Cracking off the injectors won't tell you the full story, you need to know if there is excessive leak back from each injector. If there is an internal fault with an injector the fuel goes in the high pressure side and straight out of the return NOT into the engine.