Hey so I just finished changing the head gaskets on my 2003 350z and it ran fine for a while. But recently I got a cylinder 5 misfire and random points. I could drive to work fine and nothing would come up, but when I came home I would get a check engine light and hear the misfire. And on the trip home it would stop misfiring for a little but then go back. So I checked the spark plugs to make sure they were all good and I noticed that they were loose. So I tightened them thinking that was the problem. I put everything back on and started it up and when it was idling the car shaked badly at idle and a whole bunch of smoked was coming from the back of the left bank of the engine and the engine code changed to a p0300. If anyone can help that would be great.

My car and 140,000 miles and like I said I just changed the head gaskets so I'm might have messed something up in the process.

 

Why did you change the head gaskets? Did you have the heads checked or redone too?

The bad shaking at idle after changing spark plugs sounds like you cris-crossed some coil packs... cylinders 4&6 are easy to mix up.