Nissan Repair: 88 Pulsar running rough -edited, air filter assembly, mass airflow sensor

Question
Hi,I have a 1988 16 valve automatic 1.8 dohc Pulsar.
My car sounds like it is running to rich? when i give it gas it runs rough and then i hold it steady at one rpm it seems okay,then when i let off the gas it backfires.

Its kind of like driving with the choke on
i have changed the plugs,o2 sensor[had a elec 4 wire one on ,was wrong one]
Any assistance is greatly appreciated

I replaced the fuel filter and it ran GREAT,and had lots of power.....for 45 min then as it was idling it returned to its rough ways.Like when my Ranger had a dirty mass airflow sensor,it was rough and down on power.
I put in  a full tank of gas and added some fuel additive that cleans fuel ,fuel tanks,lines and valves etc. Removed the air filter assembly and noticed what looked like oil at the bottom of the butterfly valve with dirt particles,I sprayed some throttle body cleaner into there with the car started.
I also removed a blck electrical assembly from the side of the housing there [just below where it says eccu] the revs change when you move this.I lost the bottom screw and not sure if i tightened the top properly.On the drive home on the freeway it was running the worst it ever has and was way down on power.
Any suggestions what happened? why it worked then didnt?
I just bought this car for my son to get his learners on soon.


Answer
Brock,

I would check the fuel filter again.  You might have contaminated fuel and the filter is plugged again.  Also, check the fuel pressure with a gauge to see if you are getting the proper pressure.  Check the ecu for any codes too.  Get a Haynes manual to get the pressures and the list of codes and email me back with what you find.