2001 Nissan Sentra 1.8L with 189,448 miles, I replaced the bad MAF sensor with a good name brand Bosch one even though my gut instinct told me maybe a cheap ebay one would suffice, but alas that fixed the car not wanting to crank at all when I got it. I'm not an expert, new to cars period, although I have literally fried my brain reading the litany of things that can cause rough idle/misfires in these older Nissans which seem to be very common from reading the depths of google and youtube.
The thing is....the car still idles rough, it has never died on me, but acts like it wants to, it idles at 750rpm but goes down to like 500 when it acts like it's going to die.
The fuel economy is horrible.
I've driven it very sparingly to the store and around town a little, about 30 miles total since I've owned it, and the gas gauge was full and now it's at halfway...that is HORRIBLE for a car that's supposed to get about 30-35mpg. The old gas guzzler 1992 chevy 2500 truck with a huge engine I used to have got better mpg than that. From google, the car has a ~13.2 gallon tank, so that would roughly give me only 5mpg....ya....that is NOT cool....at all... (google says MPG: Up to 27 city / 35 highway) so even if I had purely driven it in the city I would have only used up 1 gallon roughly so far, which is not true...it's guzzling gas like crazy.)
Parts I've tried to fix personally to fix the misfire and bad idle are: New Bosch MAF sensor, 4 new NGK Iridium IX spark plugs, 4 new coils, put BG 44K Fuel System cleaner in it
My car does NOT have a distributor cap, unlike the 2001 Altima which does oddly. I've seen a youtube video with the 2001 altima with distributor cap which has the same rough idle/misfire problem that seems so common online from my reading, but alas, my car has no distributor cap.
Parts the old owner says he put in "has some New parts ecm, battery, plugs, coil packs, intake temperature sensor, and crankshaft sensor. The bad is there is a cyl 3 misfire, engine compression and catalytic converter both tested fine so what's left is gonna be a fuel pressure problem like pump or injectors or throttle position sensor or a mass airflow sensor" The old owner told me he also changed the oil too.
(I put NGK spark plugs in since the previous owner used autolite which got bleh reviews on amazon and there were white streaks inside the old coil packs which apparently is called carbon tracking and causes misfires too)
From the horrible fuel economy problem and still having a misfire, would the complete fuel pump assembly (which I'm assuming includes the fuel filter) be the most likely solution?
I've read some and seen videos and I don't trust myself splicing wires and crimping them together with "only" getting the fuel pump by itself for 60 bucks on amazon and a 27 buck fuel filter. I'd rather get the whole new assembly even though it costs about 250-300.
But, the thing is, I'm very sick of all the trouble it's been giving me. What if this 300 dollar fuel pump assembly doesn't fix it? I saw a 1997 Toyota corolla for only 700 on craigslist that runs, and that gets way better mpg than this car would get. Also other cheap cars on there too. With brakes needing changed too which is going to run 200 at a garage plus a 300 fuel pump assembly, for not much more money I could just go ahead and get another car.......I'm several hundred in the hole on this 01 sentra already. The car was only 1000 but I've spent way more time and effort trying to fix it than should ever be required tbh. I guess on the plus side I learned more about cars in the process. I can also list the error codes I got months ago at autozone printed out, the other day with my scanner I only got a cylinder 3 misfire though.
Autozone codes: P0100 Mass Airflow sensor circuit malfunction
P0300 Multiple Misfire Detected
P0732 A/T Second Gear citcuit malfunction
P0733 A/T 3rd Gear function
P0174 Fuel System too lean (cylinder bank 2)
P0100 Mass Airflow sensor circuit malfunction ( again....?)
P0731 A/T First Gear Circuit malfunction
the transmission gear errors alarmed me badly at first but I read on one website that in automatic cars the MAF sensor actually plays into the transmission shifting, and at the time I installed the new MAF sensor, I didn't have a scanner at the time to clear the codes. Oddly enough last month I cleared all codes and even the SES light, but when I tried looking the other day I didn't see the option again to turn off the SES light (also called MIL light). The other day when I scanned I only got 3rd cylinder misfire, before I put the NGK plugs in I was getting multiple cylinder misfire....I guess the NGK plugs helped.
that's about all I got, thank you for any help. I'm leaning towards the fuel pump assembly due to horrible MPG at the moment, but I don't want to waste $300 on something that's not going to fix the problem. I've only been able to try a few things a month to try and fix it, I don't have all the money in the world by a long shot. It does run and cranks instantly and has never actually died on me while driving, but it worries me with the rough idle, and the horrible fuel economy is a MAJOR con to me.
