I have a '96 auto with 237k miles. I bought this car a few months ago, from someone who didn't take very good care of it, and wasn't very honest. But I had a '96 5spd with 609k miles and remember how amazing of a car it was, but sold it to get something else.
I found my way back to a Maxima, and this one has been trouble.
When I bought it, it ran GREAT! Then about a week later, it started to get to where it would crank, start, then die. Over and over, then I realized I could hold the pedal for a few seconds, and it would start to smooth up, and run. Also, when it would do this (randomly) it would put out a puff of black smoke (not blue) and smell like it was just dumping raw gas.
Well, then it would eventually just die at stop lights, so I took apart and cleaned the very gunky IACV, and that solved that, for the most part, it actually high idles now!
Now my issue is, it'll randomly start surging, like it's just falling on its face, and this can happen while just cruising down the road, holding speed, or while accelerating.
When it wants to die, say I'm turning into a place and I'm pushing the gas, I can usually let off, and it'll straighten up, other times...it'll just die.
I KNOW the IACV isn't the issue, I cleaned it well, and it does sometimes high idles, when it isn't acting up.
I KNOW the fuel filter is good, I just changed it out.
Sometimes this car will drive a whole day with NO issues, sometimes it'll drive good, then get back in it, and it'll start falling on its face again.
I HATE the uncertainty of not knowing how it's going to act from one trip, to another.
But I can say, it's like when it's acting up, it smells like fuel, strong. So I'm not thinking it's the fuel pump, because it smells almost like it's flooding itself out.
I ONLY use premium fuel, the previous owner...however did not.
When I bought it, the IAT sensor was missing, so I put one on it, no change other than the code going away.
I replaced the ECT sensor, as I had a Pathfinder that acted similar to this, and it was because of that sensor, but alas, made no change.

I currently have a code for:
P0136 O2 Sensor Bank 1, sensor 2 (post cat, right?)
P0325 Knock Sensor
P1400 EGR solenoid

Please help! This is driving me insane!

 

The fuel injectors can leak. They dump excess fuel. A tip off is that the car will run when you open the thottle to let more air through.

Start by removing the plugs. You should find one or more which might smell gassy and wet.

It's a good idea to replace the three rear ones all at once since the upper intake manifold needs to be removed.

The injectors can be rebuilt for a reasonable fee.

I have used Injector RX in Houston, TX. They do good work and have quick return time.

 

O2 sensors can also cause the maxima to dump more fuel and/or poor idle. If you change an O2 sensor, might as will change all 3. Sometimes, the O2 sensor will get clogged and give the ECU an incorrect reading without throwing a cel. And 1 messed up O2 sensor can mess with the others' readings.