I have bought a 96 civic coupe that recently was swapped with a 2000 crv b20b motor. It has a b18 p75 ecu, b18 intake manifold, skunk2 throttle body, some sort of headers (cannot see the brand due to heat wrap), a test pipe (No cat convert), an aftermarket exhaust system, and some sort of ebay chromed out short ram "cold air" intake.

When I bought the car it was running rough and shaking on the way home, it had 4 codes that I quickly tackled, two were for both oxygen sensors since rats chewed them. This fixed the O2 sensor codes, the next were a manual transmission speed sensor and a low voltage code, these both went away after I replaced my battery terminals since both (+/-) were cracked, PCV, Oil change, Plugs/wires, locking gas cap. I also did a valve adjustment job since the b20b was ticking LOUD (I heard these need valve adjustments quite frequently), So i set them to the original standard and the ticking went away and all is well. The car was then working fine for the next 3 days driving it to school, until I received code P0171. This code I presume didn't pop up initially due to the 02's being destroyed and now that they can finally read, told me the vehicle is running lean. I then took off the intake pipe sprayed down the TB (Didn't look bad at all), and unbolted the IAC and gave it some cleaning as well (didn't fully remove). I also sprayed down my vacuum lines with soapy water and couldn't see any bubbling or change in RPM's while doing so. I have yet to buy a shop vac, and do the test on my exhaust system before the bank 1 sensor.

Is this due to having a bigger throttle body, intake pipe, b18 intake manifold, headers, (I assume not a test pipe issue since it is after bank 1 sensor), and having a b18 p75 ecu running a b20b? This car was never tuned keep that in mind, no chip at all in it either. I read that the b18 ecu does run a little lean on b20's but that it should not trip a code. So in a sense will a socketed ecu and tune fix this issue? And yes she does run sluggish in 1-2nd gear, bucks almost always when shifting and letting up on the clutch. Any help is appreciated since this is my first honda, but definitely not my first or last vehicle wrenching on

 

If nothing is damaged or functionally inoperative, a TUNE should solve your issues. Make sure there are no vacuum or exhaust leaks that would cause the O2 sensors to make decisions from bad sensor data.