Vauxhall Zafira starts but cut out

i had problem that id juddered with varrying revs and moved sluggish, mechanic said that its coil pack and spark plugs. on his computer it said fault about exaust torque or something. i changed the coil pack and plugs but then it just starting to cut off straight after getting ignited. i have put back the old oil pack but problem persist. now i am unable to even move it. because it just cutts off after starting. have no clue to the problem.