P1409 my engine is running real rough I replaced the mass flow sensor and the idle sensor also replaced the fuel filter. it smells very rich at exhaust. I also replaced o2 sensors. I have a p1409 electronic vacuume regulator control circuit code what do I do next?

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.

You may not have all the things I list. these are things that will make an engine run rich. ECM, 02 sensors, map sensor, mass air flow sensor, vacuum leaks, throttle position sensor, Clogged air filter, Clogged catalitic converter. You have already replaced the injectors and the ECT , so that rules them out. Check for codes. Start with vacuum leaks. Hoses and the intake manifold gaskets. If you need more info let me know. Randy

The mass air flow sensor is one of the sensors used by the engine to determine th air to fuel ratio. so if you smell fuel and your engine is running rough this could be the problem.

Air filter box cover lose and sucking to much air, check to see if cover installed correct. Also could be mass air flow sensor.

Black smoke means buring rich. Have the vehicle's ECU scanned for codes and do the repair the codes describe. I'm gonna take a stab in the dark and say Mass Air Flow Sensor.(MAF)

check your throttle position sensor

The idle air control valve (IAC) may be stuck or failing. This solenoid-type device controls the airflow into the engine at idle. It is fed control input signals from the engine's computer. Over time, the IAC valve may become dirty from EGR gases and carbon, etc. It may have a worn pintle (valve head) or the return spring may be weak or broken, causing a rough idle or even stalling from an over-rich fuel/air mixture. The second thing to have checked is the throttle position sensor.TPS. These devices will "flag" a fault on your vehicle's onboard OBD-II computer, which a decent code reader/scanner can display and clear. Third, a dirty throttle body housing/venturi can cause rough idling and poor response. A special cleaner is needed to remove oil and carbon residues from the specially-coated inner surfaces of the throttle body. Fourth; you may have a Mass Airflow Sensor (MAF) that might be failing/malfunctioning. Some vehicles use these instead of the Manifold Absolute Pressure (MAP) Sensor, which you may have. These sensors need to be checked and verified that they are functioning properly. Fifth; check/change your vehicle's fuel filter, and verify proper/adequate fuel pump pressure and flow performance. Don't run your vehicle below 1/4 tank of fuel...doing this sharply reduces the life and cooling of the in-tank electric fuel pump. These are not cheap, or easy to replace!

check the actual fuel line. Also is it fuel injection or carberator

Check the fuel filter, it might be clogged.

If it is a carb engine have the air fuel mixture corrected by adjusting the screws on the carb. Try also adjusting the idling.

For EFI engines see if you can check the Idle Control Solenoid Valve, have it cleaned. You can also check the oxygen sensor if it is working or not