Most likely your alternator is starting to go bad, or your battery is starting to lose its charge in tge cold, which means its probably time to replace it.
Plug gap on SR18 is 1 mm ( .040")
From my own research on the internet I believe that all Nissan 1993 - 1998 have a Cam Chain (Timing Belt)
slow to start from cold and starts when warm
a have problems to start when it is cold
If its manufactured between mid 1980's and 1998 it won't. I'm specifically referring to the SR18 and SR20DE engines which are chain driven.
Automatic choke stuck open
how can i solve the problem
* A heat riser valve
sounds like a temperature sensor problem
You need to warm the car up with hot water.
If the choke not work properly then your car wont start in cold weather or morning times. The other reason might be the fuel section is dirty and need some service.
Nissan