My 2003 Maxima has a rough startup for an instant and then runs smoothly. This started when I had to park it in outside, cold weather. It sounded like a diesel starting up but then runs great. Nissan dealer checked everything and gave up; no computer indicators or experienced opinions. Independent mechanic thinks it could probably be carbon on the pistons; need to clean this and drive it more on the freeway and not just around town. Since I am retired and this car only has 75,000 miles it could go the duration; but I relish smooth startups !
Try this - turn the key to “on” but not all the way until it cranks - just to the point where the dash lights all come on. Then turn it back off. Then on - off - on - off about 5-6 times. Then crank it up and see if it makes a difference.
Each time you turn the key you should be able to hear a 2-3 second hum of the fuel pump. The key on-off cycles are to make sure it is getting pumped up to full pressure before trying to start. If this makes the start smooth then I think your two options are to live with it (as long as you can) or have the fuel pump replaced. Although a new fuel filter might help.
If that doesn’t do the trick, take it out on a long straight lonesome road, and start from a stop, and floor it in every gear, winding it out as far as you can. This is the quickest and simplest way to burn out the carbon build up on valves and piston tops. However, carbon build up usually causes a rought shut down, not a rought start up. This condition of rough shut down is known as dieseling.
When’s the last time the spark plugs were replaced?