2001 Vauxhall Corsa engine management light

Hope somebody can assist me please, I am the owner of a Vauxhall Corsa (2001) 1.2 SXI. The fault initially was that the engine management light was constantly on, the codes were checked and new lambada sensors fitted. The management light is still on but now flashes for few seconds and car losses power. When engine is swiched off and restarted it runs okay for a while,distance varies. Codes re-checked and shown as multiple mis-firing. Changed ignition coil, spark plugs and eg valve. Problem still exists, all suggestions welcome.