I'm still having problems with my 2001 maximum if I hold the gas pedal down at 40 miles an hour it surges the timing is holding more or less steady and the readings on the throttle position sensor seems to be okay! Can anyone help? Thank you.

HELLO EVERYBODY OUT THERE, I AM WORKING ON A 2001 Nissan Maxima, and my problem is it is hard to start and when I do get it started sometimes it will idle down and shut down. Now every time I spray starting fluid it starts up right away right on the money. I was getting a code P0172 and P0175 I did change the fuel pump and fuel filter especially when I found out that this was the original fuel filter from 2001 and the gasoline came out black. I also did change the mass airflow sensor because it was giving me problems. At first when I did replace the parts I drove the car at 60 mi./h and drove it approximately 55 miles and everything was okay until I gave the car back to my friend and a few days later came back with problems I described on the beginning of this post. I hope someone can shed some light on my situation and it will be most appreciated thank you, Sir Tony