I have recked my car...and got a new ecotec put inn...I'm reading P0340 the camshaft sensor malfunciton...and multiple o2 sensor codes...i cleared them all then the P0340 came back on...and there is also a multiple misfire code...but my CEL is not on...The car jerks...like some one is tugging on my throtle body wire...I'm also getting really bad gas milleage any where from 8-11 miles per gallon...I really need help...Should I replace the O2 sensors, or plugs/Springs...what should I do...It get worse everyday I don't fix it...Please help me...

you should print out all that information, schedule your car in at an authorized GM dealer and hand them the info. Theres a good chance they've run into situations like that tons of times and they would be your best source of help right now, to diagnose a problem of that nature over a forum is beyond difficult. Your call, but a dealer technician should look at that.