the Z34 doesn't have a 3400, it has a 3.4 DOHC. There is a difference.

As far as your issue, obviously hard starting isn't normal, i'm going to agree with you that its some kind of sensor, but i really don't know enough to say for sure.

 

thats what i was thinking.. but i thought that if it was a sensor it would have problems all the time..?

 

3400 is not the 3.4 DOHC. Check your fuel pressure also. Unplug the MAF and see if it makes any difference.