Hello, i have a cts 2003 and i just do not know what to do anymore i'm looking for any type of help.. The car started shaking hard out of no where usually only when im idle or at a red. if i put it in park or neutral it'll stop shaking. The codes are coming up saying my oxygen sensors are bad and im having misfires in my cylinders.. The mechanics are saying the misfires can be making my o2 sensores go off. I'm not sure what to do they recommend a tune which might fix the misfires. The car doesnt shake in the morning as i'm guessing the engine is not hot yet. please anything would help as a tune up is $300 and it might not even fix it.... ---a very desperate cts lover