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My Maxima misfire

I have a 1998 Maxima with 57K miles on it. I just bought it about a month ago. Anyway, a week ago I noticed It felt very “choppy” when I shifted into Drive or Reverse. It felt like it was going to stall but it never did. The Service Engine Soon light has been on for about 3 weeks but now, when I go up hills especially, that light blinks. I can still drive it but I shift into Neutral at stoplights to avoid hearing the rough idle while in Drive. Went to Pep Boys yesterday - they had the car for about an hour and then informed me that they would need to keep the car for a full day because of the “complex issues involved” - especially concerning the codes. The codes they read were:

p0300 random misfire
p0325 knock sensor
p0440 evap emission

My car passed smog test abut 3 months ago. I can drive it OK it just is very choppy and so there’s not a lot of power, especially going up hills…thanks

Allow me to suggest that a reputable independently owned and operated shop might be better able to diagnose and solve the problems than PepBoys. Our local PepBoys is great for tires, batteries, alignment, and other basic maintenance items, but they’re really not geared up for involved diagnosis.

My wild guess is that you’re struggling with a fuel delivery problem, especially involving the EVAP system. My guess is that the fuel tank isn’t venting properly, creating a vacuum as the fuel is pumped out and preventing the fuel pump from maintaining pressure. This may have caused premature fuel pump failure. This type of a problem can cause all of your codes and all of your symptoms.

HOWEVER, having taken that wild guess, you need a shop that has the gear to be testing the fuel pump, running “smoke tests” (a test wherein a smoke machine pumps smoke into the system and a diagnostician sees where it goes), testing the various valves that control the breathing of the gas tank, and other such stuff. With respect to PepBoys, they don’t equip themselves for the more in-depth analysis. Their business model is focused on the more mundane (but no less important) stuff.