yeah engine shaking at times could be a miss fire. check the gaps on your plugs. maybe your 02 sensor is bad but i doubt it. possibly the header but from what i read on the thread it shouldnt affect anything....sure am glad we dont have smog tests in texas. the refinery plants produce way too mutch toxics to care abotu our cars lolga16de6669 said:my 1992 sentra e wont pass smog. i did plugs wire roter cap oil and cleaned my k&n filter. was a 216 at idle of hc after tuneup its now a 350 wtf. any ideas? i have an underdrive pulley and header. i cant for the life of me figure it out. the smog dude mentioned misfireing but i cant hear it, only the engine shakes funny a couple times a minute. any help make me happy.