What are the causes for NXo reading - 1988 Toyota MR2

There are a few things that may cause the display of error code P0449. The first and most likely cause is the dysfunction of the vent valve in the EVAP system. The second possible cause may be a connectivity issue regarding the connection, wires, or circuits of the EVAP system that results in a false reading. The third and final potential cause may be a faulty PCM, ECM, or EMC which is causing a false reading.

https://fuse-box.info/chevrolet/chevrolet-s-10-1994-2004-fuses-and-relay

probably no-- as a faulty cat converter will spring an O2 code
however if the flex part of the exhaust pipe is cracked near the manifold ( cracks inside the stainless weaving) that will affect the HO2S sensor ( heated oxygen sensor)
The exhaust gas will be escaping and passing under the car causing everything to get hot
The HO2S sensor is responsible for reading the exhaust gas composition and reporting to the ECM and if that reading is not within parameter from the crack, that will cause the readings from sensors you mentioned to be reporting wrong

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P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replace the air filter and clean the air flow meter. If the problem persists the front oxygen (O2) sensor may need to be replaced.
The P0174 code could also be caused may be caused by one or more of the following: debris on MAF sensor causing an incorrect reading, improper oil level, low or high fuel pressure or Engine Control Temperature (ECT) Sensor reading inaccurate.

Possible causes
- Intake air leaks
- Faulty front heated oxygen sensor
- Ignition misfiring
- Faulty fuel injectors
- Exhaust gas leaks
- Incorrect fuel pressure
- Lack of fuel
- Faulty Mass Air Flow (MAF) sensor
- Incorrect Positive Crankcase Ventilation (PCV) hose connection Help with this Tech notes
If the P0171 is combined with the P0174 code, it's very likely that the problem is caused by an intake leak. If there are no intake leaks, the next step is to replaced the air filter and clean the air flow meter. If the problem persist the front oxygen (O2) sensor may need to be replaced.
The P0171 code could also be caused may be caused by one or more of the following: debris on MAF sensor causing an incorrect reading, improper oil level, low or high fuel pressure or Engine Control Temperature (ECT) Sensor reading inaccurate.

Read more: http://www.helpforcars.net/obd_codes/p0171_chevrolet.html#ixzz3tjvehfyV

Yes, a bad map sensor causes poor acceleration, but don't assime the sensor is bad. First check to see if manifold vacuum is getting to the sensor. If yes, next verify that the reference voltage (5vdc on most cars on one of the wires--key on) is getting to the sensor. If yes, then test the sensor by a applying suction to the port and reading the output. You can use your scanner for that.

The cause is either the EVAP purge valve is stuck open not closing off the engine vacuum source to the fuel tank. The EVAP vent valve is stuck closed, not allowing the vacuum in the take to be released causing a vacuum reading when there isn't supposed to be one. Or the EVAP fuel tank pressure sensor is always reading vacuum even if there is none causing a false reading. Also make sure to disconnect and reconnect the connectors for these components to rule out dirt, dust, and grime getting into the pin terminals causing problems like this. These components are located on or near the EVAP charcoal canister.

I hope this info helps!
~subyguru~

it could be a bad O2 sensor.

it could draw cold air back onto your valves or it could cause your oxygen sensor to read a false lean reading causing the computer to add fuel and damage the catalytic converter.