Runs too rich & surges. O2 sensor is good. how do you test the fuel regulator and the mass air sensor?

lots of causes , injector leaks sure. is one of many.
this is EFI and EFI only controls injection.(and spark)

it and all its inputs. do. called sensors.
1998 car in usa the scan tool tells you what all sensors are doing,called PID scans and DTC errors of any kind
25 year old car. and engine and all parts on it.

ALL fuses good?
NEXT:
scan the PCM see P03xx error or others? (scan it)
p0171 And P0174? P03xx codes and more do the scans.
engine good first. for sure this OLD.
we do engine tests.
compression over 150psi on all 8 cylinders.????
vacuum gauge at 20" HG at idle and not BOUNCING
we use tools to find cause. gue$$ing can be endless and super expensive or worse adding on wrong parts.
SPARK:
8 spark plugs all new, and all 8 COP boots new
boots never every lasted, 25years, nor spark plugs
and last fueling , cant burn fuel correctly with bad engine or bad spark CAN not.

SENSORs and stuff:
MAF SENSOR BAD OR WEAK, OR NEVER CLEAN IN 25 YEARS WILL RUN LEAN .
FPR 25 YEARS OLD ARE BAD. THEY ALLOW FUEL PRESSURE TO BE CRAZY TOO HIGH OR LOW
CALLED OUT OF SPEC. (or gets stuck at max PSI)
THE VACUUM HOSE TO FPR MISSING FUEL PRESSURE WILL BE WAY WAY TOO HIGH and super RICH BURN.!
IF FPR VAC NIPPILLE IS LEAKING FUEL IT IS BAD.
Fuel Pressure Engine Running kPa (psi) (28-45)
Key On Engine Off kPa (psi) 35-45)
THIS SPECS ARE DECEIVING,
EFI LAWS, KEY ON PRESSURE IS ALWAYS HIGHEST PSI. (DUE TO ZERO VACUUM)
AND RUNNING ENG AND VACUUM MAX INCHES HG, IS LOWEST PSI FUEL;. IF NOT RUNS RICH AS A PIG.
KEY ON PRESSURE FPR IS 5 TO 6 PSI FUEL LOWER THAN AT IDLE. <THAT IS ITS A#1 TOP JOB THIS.

EXAMPLE 40 PSI KEYON PRESSURE.
THE IDLE WILL BE ABOUT 35.(20 "HG IDLE)
THE FPR DOES ALL THAT.
IF NOT ALL INJECTOR , OVER OR UNDER INJECT.
PERSONALLY I NEVER EVER TRUST ANY OLD FPR. I HAVE HAND VACUUM PUMP TO TEST IT FULLY. AND HAVE FOR 4DECADES.MID 1980S

INJECTOR LEAK DOWN TESTS FAIL OR INJECTOR BALANCE TEST FAILS ,TOLD IN SM= SERVICE MANUAL.
BASICS BAD: IS THIS:
THERMOSTAT BAD. OR MISSING, OR NOT AT 180F TO 200F TEMP STUCK AT 150F BAD BAD BAD.

ECT BAD, SHOWS 150F WHEN COOLANT IS 180F
CAUSING:SUPER RICH INJECTIONS.
SO PCM IS STUCK IN COLD STARTUP MODE FOR EVER AND BURNS FUEL LIKE MAD.

SURE O2 SENSORS DEAD OR EXH CRACKS NEAR BY THEM MAKES THEM LIE AND EFI GOES HOG WILD RICK. SURE.

WHY NOT SCAN THE PCM FIRST.
AND SEE WHAT IS WRONG FIRST.
SAVE TONS OF GUESSING

LAST AND NOT THE LEAST
YOU CAN SCAN ANY PCM AND SEE IF IT IS IN LIMPHOME MODE AND IF IS, IT BURNS FUEL LIKE CRAZY
AND SEE TOO ,CLOSE LOOP MODE IS DEAD
FULLY HOT ENGINE.
YOU CAN SEE LTFT EFI IS STUCK FULL RICH.
AND DTC ERRORS ,LOTS?
THIS IS NOT GUESS IT IS TESTING USES REAL TOOLS. TO FIND CAUSE.

Year make model???? A rich running engine can be caused by
Defective/stuck EGR valve
Defective/sticky fuel injector
Leaky (internal) fuel pressure regulator
Map sensor
Coolant sensor
Mass Airflow sensor
O2 sensor stuck lean (giving false reading)
Bad computer
Have the vehicles operating parameters scanned to monitor sensor operation and values to determine what may be causing this rich condition before throwing your money at unnecessary parts replacement

Its always a good idea to double check codes especially with sensors, if its the heater circut replace o2 if its out of range reset and see if returns

O2 sensors reads the amount of left over fuel in the exhaust and converts to a voltage signal so when voltage is around .800mv this is a rich condition and computer is commanding less fuel and .200mv is a lean condition computer is command more fuel. for rich condition problems check the following components. Fuel pressure regulator, leaking injectors, mass air flow meter, engine coolant temp sensor, map sensor.for a lean condition check engine vacuum leaks, exhaust leaks, air injection, map sensor, mass air flow sensor,fuel pressure regulator, fuel filter,injection

Did you check fuel pressure after replacing the pump ?
If the regulator fails, it would either not maintain normal pressure, or leak fuel into the vac hose.
If the mass airflow meter fails, it won't run and the check engine light would be on.
Have you watched the O2 sensor and engine temp sensor on a scanner to see what they are reading ?

Check the fuel pressure regulator for fuel in its vacuum hose.If there is fuel in the vacuum hose coming off the regulator then replace the fuel pressure regulator.If it checks out to be good then i would check the coolant temperature sensor because it will cause this problem also.

My guess would be a fuel injector or fuel pressure regulator problem, or a Mass air flow sensor.
The O2 sensor does not come into play until the engine has run for a couple of minutes.
Is the check engine light on ?

This means its running rich, burnning to much gas. this could be due to a bad mass air flow sensor or bad o2 sensors or even a bad fuel pressure regulator, i would start with the fuel pressure regulator, remove the vacuum hose that goes to it and start the engine and see if gas is leaking from the port that vac hose goes to and if it is then replace that regulator and see how it runs from there. the rest you will need a scan tool to check the readings of the o2 sensors and mass air flow sensor. another thing is that if the engine is running rough it may be misfiring , skipping due to bad wires or sparkplugs. white smoke means alot of gas is being burnt and a regulator would be the first thing i would look at. good day.

CODE ???? If you would like help need to know what code ? P0172 ?
Using a scan tool an checking scan data would be the first thing to do , before replacing parts ! That's a rookie move. What are the fuel trims at ? is the PCM adding ,taking away fuel ? Are the O2 sensors switching rich to lean like thier suppose to. Using a better scan tool an looking at data , an freeze frame data .
003 Freeze Frame and Conclusion

009 Testing DCTs
You could have leaking injectors , clogged air filter , bad fuel pressure regulator , mass air flow sensor bad . You wan't fix cars , learn how.

o2 sensory ???? ha ha ha lol . it's O2 sensor Suggest you take it to a qualified repair shop . Because you have no clue .

PO171-System to Lean (Bank 1)

Air filter cover tight?
All intake ducting tight?
Clean MAF Sensor.--CRC MAF Cleaner
Fuel Pressure Regulator?
EVAP Purge Valve-stuck open?
Vacuum leaks?
EGR System-issues?

Seems your getting a lean O2 Code,because it is trying to correct for a rich condition,as you said.

Is the Throttle Position Sensor-original?

Work on what is driving it rich,my list is a possible.