No power/limp mode?

Recently bought a vauxhall astra 1.7 dti estate 2003, as soon as got to drive it realised that accelerator did almost nothing, flat to the floor in any gear takes at least 3 or 4 seconds for the car the begin revving properly, in second or third takes 10 maybe 20 seconds to crawl up to about 3000 rpm at which point it does boost very slightly. Once into 4th or 5th gear, keeping the rev's above 2 and a half is almost impossible even on flat ground and will drop speed. The only fault code flashing up is 0100, wondering if a dodgy afm sensor could be causing this issue?? Any advice appreciated as car is only method of getting to and from work and half hour journey is taking closer to an hour...