2003 Nissan Sentra GXE starting problems

2003 Nissan Sentra GXE starting Problem:

I am having big issues starting the car the first time I am trying to start it. Once I successfully start it up it starts at the first time I crank it the second time and third time.
But until I get it started it takes 10-15 minutes, sometimes it just fires immediately.
The first one mechanic said it is the knock sensor because it came up with a knock sensor code...I exchanged it (now there are no codes showing up anymore) and it still does the same thing. After a month the car did not start at all anymore.
I called another mechanic he said it is the fuel pump...exchanged it, but I still have the issue...not as bad it takes now 5-10 minutes.
He says I should have ordered the fuel filter as well. I did not see any fuel filters to order for these cars and it did not come with one.

Can anybody out there help with this issue? I am really frustrated with this car since I payed 5k for it.

What is the problem with this car?
Are there single fuel filters to buy for these models?

Thanks a lot in Advance,
cet

The key here is that it's hard to start after sitting.
I'm going to guess that the fuel injectors are leaking, and when it sits for a long period of time, they leak enough into the engine to flood it and foul the plugs.

Ok, what do you think that fuel injectors cost and what do I have to pay in labor for a job like this?
Would you recommend keeping this car or get rid of it?
Thanks for your help.

Whuohhhhh........I don't know anything about this car, but I can't imagine it not being worth putting some money into. What does it 'blue book' for? What will it cost to replace? What is it's overall condition? Can you get a definite diagnosis for $100 - $200? Won't be worth anything to be hasty.

the kbb value is around 4500-5000$...Overall condition is good. It has new paint. Engine looks great and when it runs it's like new.
I went already to 3 mechanics...so it is hard to be sure I guess.

It's a tough one. Only you can decide.

Good luck.

This morning it started up right away.
I guess I'll have to try it for a while and see what happens. Maybe I'll exchange the fuel injector and spark plugs next and see.

Can I do it my self (fuel injector) or is that too difficult for me (no experience at all)?

Thanks foe all your input.

cet

Again, not knowing anything about this engine, most commonly fuel injectors are are individual units on each cylinder, much like the spark plugs.

These aren't particularly difficult to change but I don't know if I would recommend it for a first time DIYer. Also, quite often the pintle end the very inner tip of the injector) can be cleaned and they work good as new. But again, there is a wiring connector involved, a retaining device involved, an 'o' ring seal, etc., etc., etc,.

Thanks for the info...