Vauxhall Zafira intermittent misfire and loss of power

Hi all My zafira suddenly started to missfire last week it is ok when the engine was cold but as soon as it began to warm up the problem starts. I changed the plugs, someone said do an oil and filter change which i've done but no luck. the engine management light came on so i disconnected the battery for 20 mins to reset it. After doing this the missfire only happens if you acelerate normally and only up to about 30 mph if you acellerate gently or are going over 30 the engine is fine for a while but then the management light comes on again and the misfire gets worse and happens at all rpm. i was told to blank off the EGR valve which i tried but it's not made any difference. I tried to check the fault codes by pressing my feet on the brake and acellerator pedals and counting the flashes of the light on the dash and i am getting 10, 3 10, 3 10 3 10 10 which i think translates to 0303 0300 am i correct?
Anyway short of admitting defeat and taking it to a garage where it will more than likely cost a bomb i don't know what to do next so any suggestions would be most welcome. oh I the EGR valve went faulty and was changed about a year ago.