I have a '02 Nissan Altima 2.5 SL 4 cylinder

her is my problem hard time starting my car cold or hot check engine light is on reads Po335 (crankshaft position sensor malfunction) also (can't remember the code #) vehicle speed sensor Steps i have done 1.change the crankshaft sensor 2. clear the codes turn the car on and no check engine light but i plug in the obd II (from auto zone) and i still have one code present Po335 drive the car for about 30 min and then the engine light comes on. I plug the scaner after i have driven the car vehicle speed sensor code is present again 3. change the plugs 4.check fuel pressure its at 50-51 psi (good) 5. I tried checking the spark from the wire i don't have the right tool for that so i used a screwdriver to metal i had some one crank the car but the time frame were its having trouble i did not see spark till it actually started to run and i tried to do the same to another wire but i could not do it because of room

once the car is on and running i have not had it die out on me drives like new