Vauxhall Astra p0170 code amongst other problems

hi ive posted a few times on here and have had great advice..i now have another problem for those who dont know the history i will give u a rundown and post the latest problem at the end:


i drove over something which ripped my exhaust off and punctured fuel tank a modified fuel tank was sent for my mechanic to fix, it came with an extra pipe he didnt know how to fit with extra pipe has left one of the pipes off apparently its a breather pipe which is meant to go to carbon cannister...my mechanic said that my cannister doesnt need one?? engine management light kept coming on first it said fuel rail(something like that or fuel trim) then it said cylinder 4 misfiring then it sounded like i was driving a helicopter so changed coil pack light has stayed off for a week now but today of all days its come back on since yday intermittent smell of petrol, and sometimes car feels sluggish foot to the floor and struggles to get to speed sometimes judders in lower gears, and sometimes its fine goes a bit noisy when need to change gears also thought it may be coz it was a cheap exhaust the noise...dont yet know wat the fault code is sayin but getting sick of it now...another mechanic cleaned the throttle the other day as i got a second opinion he also said the other week that my injectors need cleaning...my original mechanic said they dont as its petrol and also my fuel tanks was plastic...any ideas anyone...i have bought some redex (i think thats wat its called) i havent used it yet is it worth to clean injectors??...also when i turn engine on the revs are just over 1000 in idle and sometimes goes 1250 and back 750 and up again whilst still sat in idle when turning engine on after been off for a while..

the latest problem is today my mechanic looked on diagnostics and its coming up with code p0170 fuel trim bank 1..he is scratching his head, he seems to think the smell of petrol is in my head and makes a joke out of the vibrating coming from my seat gear stick and steering wheel!!...he seems to think that my temperature gauge sensor may need replacing??...and thats it!! please someone shed some light its driving me mad (excuse the pun)