loss of power during exceleration?

i have a W reg astra mk4 sri and notice that it is not as owerful as it should be. lack of acceleration power is most noticing. small amounts of blue/white smoke comes from my exhaust when starting up and running. no popping or missfiring or trouble starting up. recently changed plugs, all filters and dropped oil. plugs were wet. any ideas to what the problem is?

ian hogg
October 2009