[Jeff]

I think it's a bad coil...you have a '99 and they are well known to have bad coils.

Since you don't have a code you can try pulling each coil, one at a time, and see if you can find the coil that is bad. You could also check each coil with a multimeter to see if one is registering incorrectly.
(though testing each for ohms has proven unreliable, fyi)

 

[Jeff]

Just an fyi about the Maxima...head gasket problems are fairly rare.

I'm willing to bet it's definitely the coils.