I just picked up a 2004 g35 sport for a good deal with an engine hesitation and here is what I know..

When I driven it hesitates and bucks a little in the low rpm range. I only drove it once then the snow started to fly.
I let it idle in the garage for a bit and the temp didn't come up till I put on the heater then it jumped right to the middle but still no heat coming out of the vents.
I checked the coolant and there was none visible in the radiator.
The previous owner told me that he did find coolant in the oil and he changed it a couple times.
I checked the oil and it's a nice golden color
I opened the oil filler cap and it had a white substance clinging to the inside.
Everything aims to a possible head gasket but it doesn't blow white smoke. Any ideas what it could be or a direction to go To diagnose it more definitively?
Thank you.

 

Any ideas?

 

Is it an auto or a manual? If if's an auto, are you using the manual shifting mode?

 

It's a 6spd

 

have you checked the transmission fluid? You may have a leak. Or it might be the transmission itself. Before assuming that though, consider that it can also be an issue of a bad fuel pump, O2 sensor, or loose spark plugs. Have you checked those?

 

also check for coolant leaks in the hoses and connections. does it go through coolant fast?