Peugeot 307: If your car does start normally in first attempt then Glow plugs doesn't play a role to cause limp mode. There are several other reasons including turbo waste gate actuator, EGR solenoid problem, diesel pressure drop or any single injector is not working. If the Engine management light is on then definitly there is a trouble code registered by ECU. Let diagnose your car and read the fault code to narrow down the problem.
Wahsteam
October 2011