pleas help!!! i've got v reg vectra 2.5 v6 manual which was running lumpy as you like giving symptoms of cat failure (lack of power, pressure build up in exhaust hissing out etc) , so i've changed cat along with both lambda sensors and done full service. ran like a dream for about 100 miles and now running same as before. know its not a miggy but hoping someone will know what it could be so i will also know what to do if my miggy does the same!!!!