97 240sx runs rough for a minute when started

[SlidnSideways]

The problem just occurred this morning. The car ran fine last time I drove it (2 days ago). I put new tires on it yesterday. This morning when I started it, it was shaking similar to the way it would shake if it was only firing on 3 cylinders. After about a minute of running, the shaking goes away and it runs smooth again. The only other thing I have replaced fairly recently was both of my o2 sensors about 2 months ago. Anybody have any clues?

Thanks!

[MaximA32]

Check the IAC/V. Clean if needed.

[carmo]

Sounds like a headgasket leak to me. check your coolant to see if it's low.

[the technican]

i second the headgasket, im sorry to tell ya..does it smoke if you rev while its running rough, and is it white smoke. if it is thats whats wrong