P0174 Error Code

My 2000 Ford Windstar has check engine light on and the error code "P0174- System Too Lean". I tried to clean the MAF, and temporarily the light went off. Now the light is still on and I get about 8 mpg around town

Scan the computer again might not be the same code that causing the CEL to come on. If its the same code check the following below

Lean fuel condition could be caused by one of the following below:

1.Vacuum leaks
2.EGR and PCV valve.
3.Low fuel pressure.
4.Dirty fuel injectors.

Read the guide below on vacuum leaks, it will help you figure this out. That is usually what is wrong with these

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge

If this is a 3.8 engine, there I a TSB concerning the isolator bolts and a couple other things.

Here is the TSB

Article No.
03-16-1

08/18/03
DRIVEABILITY - DIAGNOSTIC TROUBLE CODES(DTCS) P0171/P0174 STORED IN MEMORY -
VEHICLES EQUIPPED WITH 3.8L ENGINE

MALFUNCTION INDICATOR LAMP (MIL) - MILILLUMINATED WITH DIAGNOSTIC TROUBLE
CODES (DTCS) P0171/P0174 STORED IN
MEMORY - VEHICLES EQUIPPED WITH 3.8L
ENGINE

FORD:
1999-2003 WINDSTAR

This TSB supersedes articles 03-4-7 and 00-21-8.
ISSUE
Some vehicles may exhibit a check engine light on and lean Diagnostic Trouble Codes (DTC's) P0171/P0174 (system too lean bank 1 or 2) stored in memory.

ACTION
Do not replace PCM (Powertrain Control Module), MAF (Mass Air Flow), or HEGOs (Heated Oxygen Sensors), as these parts are not the root cause of the lean codes conditions described. Refer to following Service Procedure for details.

SERVICE PROCEDURE

These conditions may be caused by a loose fitting on the fuel pressure regulator vacuum line on the intake manifold end and/or leaking isolator bolts/port gaskets in the lower to upper intake manifold mounting area. This condition is sometimes intermittent and may not be apparent on a warmed-up engine.

If the vacuum line from the intake manifold to the fuel pressure regulator is loose at the manifold (due to oil contamination), replace the vacuum line (9E498) and install a new design LH service valve cover (6582). Another vacuum leak source is the gasket (9H486) between the upper and lower intake manifold assemblies caused by a loss of tension at the isolator bolt assemblies (9S479) due to contamination of the rubber grommets from excessive oil pullover.
1. Perform self test, if codes P0171, P0174 are the only codes stored in the PCM then continue with this article. For any other codes, follow the normal diagnostic procedures found in the PC/ED Manual.

2. (ALL 1999-2003). Reprogram the PCM (Powertrain Control Module) with the latest calibration, WDS B26.2 release or later. Do not replace the PCM. Reset the keep alive memory.

3. (1999-2001 ONLY). Inspect the vacuum line from the intake manifold to the fuel pressure regulator for looseness, leaks and/or oil contamination and replace Vacuum Line (XF2Z-9E498-DD) if required.

4. (1999-2000 ONLY). Inspect the LH Valve Cover, it should be a (3F2Z-6582-BA) Install a new LH Valve Cover if required, refer to Workshop Manual Section 303-01 Valve Cover-LH. (Refer to the following NOTE for description of the old style valve cover).

NOTE USING A SHOP LIGHT OR FLASHLIGHT, CHECK THE LH VALVE COVER TO SEE IF IT HAS ALREADY BEEN UPDATED TO THE LATEST LEVEL. REMOVE THE PCV VALVE AND RUBBER GROMMET FROM THE VALVE COVER AND LOOK THROUGH THE HOLE AT THE INTERNAL SHEET METAL BAFFLE. THE OLD STYLE VALVE COVER BAFFLE HAS A 3/16" DIAMETER HOLE IN THE 5:00 O'CLOCK POSITION AS YOU LOOK THROUGH THE PCV HOLE (FIGURE 1). VALVE COVERS FITTING THIS DESCRIPTION MUST BE REPLACED.

5. (ALL 1999-2003). Remove the upper intake and replace only port gaskets (9H486) and isolator bolt assemblies (9S479). The new isolator bolt assemblies use a rubber material that is green in color, do not use the old isolator bolt assemblies with the black rubber material (XF2Z-AA). Do not replace any other intake parts (black plastic or aluminum) or the lower intake gaskets, (9439 and 9A424/425) or the upper intake clamshell gasket (9461). Refer to Workshop Manual Section 303-01, Intake Manifold-Upper.

6. (ALL 1999-2003). While the upper intake manifold is removed, check the Exhaust Gas Recirculation (EGR) orifices that are pressed into each primary port of the lower intake manifold. If any of the orifices are plugged with soot, clean and unplug them with a pick and solvent.

CAUTION DO NOT USE SMOKE DETECTION, PROPANE GAS, OR CARB CLEANER TO TEST FOR VACUUM LEAKS. (CARB OR BRAKE CLEANER MAY CAUSE INTAKE MANIFOLD RUNNER CONTROL (IMRC) BEARING FAILURE). SOME LEAKAGE FROM THE IDLE AIR CONTROL (IAC) OR EGR VALVE AND IMRC SEALS IS NORMAL. DO NOT REPLACE THESE PARTS, ESPECIALLY THE LOWER ALUMINUM INTAKE MANIFOLD.

NOTE THIS CONDITION COULD ALSO BE DUE TO WARM AMBIENT TEMPERATURES AND THE USE OF WINTER GRADE FUELS WHICH HAVE VERY HIGH VOLATILITY AND MAY BOIL IN THE FUEL LINES (VAPOR LOCK) DURING A SHORT HOT SOAK. OXYGENATED FUELS WILL AGGRAVATE THIS CONDITION. IF NON-OXYGENATED FUEL IS NOT AVAILABLE, USE MID/HIGH OCTANE FUELS WHICH HAVE LOWER VOLATILITY AND MAY HELP ALLEVIATE THE CONDITION.

The smoke test is a legit test. They were correct about the valve cover, however not replacing it did not cause this issue. It is very uncommon for the leak to occur where it did, but not unheard of. The rod that runs through the intake is part of the Intake Manifold Runner Control. There is an o-ring there that cannot be replaced except with the lower intake. I ran into this concern once myself. But only the lower intake and all related gaskets should be replaced. There is no need to replace the upper intake manifold. It does seem odd though that you would get both codes for only having a small leak on one side of the manifold. Are they sure there are no other major leaks? If you just recently had it serviced, check the rear of the intake tube--there is a small plastic tube that connects into it that often comes off when the air filter is inspected or replaced.

Its not o2 sensor it a vacuum leak / mass air flow sensor
vacuum leak u may have to use a smoke machine to find it
good luck

MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - SYSTEM LEAN DIAGNOSTIC TROUBLE CODES (DTC'S) - SERVICE TIPS
TECHNICAL SERVICE BULLETIN
Reference Number(s): 04-17-4, Date of Issue: September 6, 2004
FORD:2000 Contour; 2000-2002 Escort; 2000-2003 Escort ZX2; 2000-2004 Crown Victoria, Focus, Mustang, Taurus; 2002-2004 Thunderbird; 2000-2003 Windstar; 2000-2004 Econoline, Excursion, Expedition, Explorer, F-Super Duty, Ranger; 2001-2004 Escape; 2004 Freestar; 2000-2004 F-Series
LINCOLN:2000-2002 Continental; 2000-2004 LS, Town Car, Navigator 2002-2003 Blackwood 2003-2004 Aviator
MERCURY:2000 Mystique; 2000-2002 Cougar; 2000-2004 Grand Marquis, Sable, Mountaineer; 2004 Monterey

Related Ref Number(s): 04-17-4
ARTICLE BEGINNING
DESCRIPTION
MALFUNCTION INDICATOR LAMP (MIL) ILLUMINATED - SYSTEM LEAN DIAGNOSTIC TROUBLE CODES (DTC'S) - SERVICE TIPS
ISSUE
This article is intended to aid in diagnosing DTC's P0171, P0174, P1130, P1131, P1150, P1151, P2195, or P2197 (system lean or lack of HEGO switches) when a vacuum leak is present. HEGO sensors, MAF sensors, and PCM replacements are not an effective repair when a vacuum leak is causing the above DTC's.
ACTION
Perform the following inspections/repairs when the above codes are found in memory. Procedure provides instructions on how to make comparisons of the total fuel corrections (using scan tool or equivalent) at idle and high RPM's to help determine if a vacuum leak is the root cause of the DTC's.
SERVICE PROCEDURE
NOTE:FREEZE FRAME AND ADAPTIVE FUEL VALUES (ASSOCIATED WITH "LONGFT" PID) WILL NOT BE AVAILABLE IF A KAM OR OBDII RESET WAS RECENTLY PERFORMED.

NOTE:FREEZE FRAME DATA WILL INDICATE THE ENGINE AND AMBIENT CONDITIONS WHEN THE DTC WAS SET. THESE ARE IMPORTANT BECAUSE THE VACUUM LEAKS MAY OCCUR ONLY WITHIN SPECIFIC TEMPERATURE RANGES AND MUST BE DUPLICATED TO DETECT THE LEAK.

NOTE:FUEL TRIMS AT IDLE ARE PARTICULARLY SENSITIVE TO VACUUM LEAKS SINCE THE UN-METERED AIR "LEAKAGE FLOW" IS A HIGHER PERCENTAGE OF TOTAL AIRFLOW AT IDLE THAN AT PART THROTTLE. THE BAROMETRIC PRESSURE (BP) PID IS NOT RECOMMENDED TO VIEW WHEN DIAGNOSING A VACUUM LEAK. BP IS AN INFERRED PID CALCULATED DURING HIGHER ENGINE LOADS.

Perform preliminary inspection, retrieve and record DTC's and Freeze Frame Data. DO NOT PERFORM KAM RESET OR OBDII RESET (CLEAR CODES) AT THIS TIME, ADAPTIVE FUEL TABLES MUST BE INTACT FOR THIS PROCEDURE.
If DTCs are continuous, or if other DTC's or drive symptoms are present other than at idle, diagnose and repair those codes/symptoms first.
Perform visual inspection - look for disconnected/broken/cracked vacuum hoses especially near vacuum trees. Check PCV elbows for cracks or loose connection. Confirm vehicle has the correct PCV valve installed. If a suspect vacuum leak is found proceed to Step 4.
NOTE:EACH VEHICLE APPLICATION REQUIRES A PCV VALVE CALIBRATED FOR THAT VEHICLE. MOTORCRAFT PARTS ARE STRONGLY RECOMMENDED. ALSO, THERE WILL BE A NORMAL VARIATION IN FUEL TRIMS FROM VEHICLE TO VEHICLE.

Determine if vacuum leak is present.
Set up scan tool to monitor the following PIDS: ECT/CHT, LONGFT1, LONGFT2, SHRTFT1, SHRTFT2, IAT.
Start the engine and run at idle with all accessories off - gear lever in Neutral/Park.
Run engine until ECT/CHT matches the corresponding freeze frame data from Step 1. This will duplicate the customer's engine operating temperatures when the DTC was set in memory. Hood may remain open during this test to help reduce ECT/CHT/IAT temperatures. Keep IAT below 115 ° F (46 ° C).
Record LONGFT's and SHRTFT's.
NOTE:TO PREVENT HIGH ECT/CHT AND IAT TEMPERATURES IT MAY BE NECESSARY TO PERFORM THIS TEST WITH THE ENGINE RUNNING FOR SHORT INTERVALS, ESPECIALLY WHEN AMBIENT TEMPERATURE IS ABOVE 85 ° F (29 °C). USE OF A GARAGE FAN WILL HELP TO KEEP ENGINE TEMPERATURES STABILIZED DURING TEST. IT MAY BE NECESSARY TO RUN THIS TEST AT SPECIFIC ECT/CHT/IAT TEMPERATURES, REVIEW FREEZE FRAME DATA. EXAMPLE: IF ECT WAS AT 160 ° F (71 ° C) THEN ENGINE MAY NEED A COLD START TO DUPLICATE THIS TEMPERATURE.

Determine total fuel correction at idle for an in-line 4 cylinder engine or bank 1 of a V-engine by adding LONGFT1 to SHRTFT1. Determine total fuel correction for bank 2 of a V-engine, by adding LONGFT2 to SHRTFT2.
NOTE:MAKE SURE ONLY THE CORRECT BANKS AND TRIMS ARE ADDED TOGETHER (DO NOT ADD LONGFT1 TO LONGFT2 OR LONGFT1 TO SHRTFT2.)
EXAMPLE 1: BANK1 LONG FUEL TRIM; LONGFT1 = +13% AND SHORT FUEL TRIM; SHRTFT1 = +23%. THE TOTAL CORRECTION ON BANK1 IS +36% (13%+23%=36%).
EXAMPLE 2: BANK2 LONGFT2 = +24% AND BANK 2 SHRFT2 = -3%. THIS TOTAL FUEL CORRECTION ON BANK 2 IS +21% (+24% -3%= +21%.).

A TYPICAL VACUUM LEAK WHICH MAY SET A LEAN CODE DTC WILL HAVE TOTAL CORRECTION OF AROUND +20% OR GREATER AT OR NEAR IDLE (DEPENDS ON CALIBRATION).

Depress and hold throttle pedal to maintain an engine RPM of 2500.
Observe PIDS with engine RPM at 2500. View and record LONGFT1, LONGFT2, SHRTFT1, SHRTFT2. Do not hold engine RPM's at 2500 for more than 20 seconds. Release pedal and repeat if more time is necessary to record PIDS.
Determine total fuel correction at 2500 RPM's by adding the LONGFT's to the associated SHRTFT's.
If the fuel correction decreases, more than 15%, (example: was +31% at idle on bank 1 but changed to +12% at 2500RPM on bank 1, a decrease of 19%) then a vacuum leak is most likely causing the lean diagnostic test codes. Proceed to Step 3.
If the total correction remains approximately the same then the lean condition is not caused by a vacuum leak. Refer to the PC/ED for further diagnostics.
Pinpointing vacuum leaks.
Monitor SHRTFT's with scan tool with engine running at idle.
Locate vacuum trees off air induction system and PCV system. Use hose clamp or pinch off pliers (avoid tools with sharp edges).
NOTE:USE CAUTION WHEN CLAMPING HOSES. A VACUUM CAP OR EQUIVALENT CAN ALSO BE USED TO BLOCK THE VACUUM SOURCE TO A SPECIFIC SYSTEM. DO NOT TRY TO PINCH OFF A HARD PLASTIC HOSE OR CONNECTION, TRY ISOLATING BY CAPPING. CLAMPING OF THE FUEL SYSTEM PURGE HOSE MAY SHIFT SHRTFT DURING PURGING MODES, USE VISUAL INSPECTION ON THIS HOSE IF RESULTS ARE NOT CONSISTENT.

Observe short fuel trims when pinching specific vacuum lines. The SHRTFT values should decrease more than 15% towards the negative direction, if a vacuum leak was pinched off. (Wait up to 20 seconds to observe if pinch has any effect on SHRTFT's).
NOTE:EXAMPLE: PINCH OFF THE BRAKE BOOSTER VACUUM HOSE (DO THIS ONLY IN PARK) AND OBSERVE SHRTFT'S. IF THE SHRTFT'S DECREASES, BY MORE THAN 15%, A VACUUM LEAK IS PRESENT. IF THE SHRTFT1 WAS AT +14% BEFORE PINCHING THEN SHIFTS TO -7% AFTER PINCHING, TOTAL SHIFT OF 21% TOWARDS NEGATIVE DIRECTION.

If vacuum leak is located proceed to Step 4c.
NOTE:INTAKE GASKETS OR MANIFOLD LEAKS CANNOT BE DETECTED BY PINCHING OFF LINES. USE OTHER LEAK DETECTION METHODS, SUCH AS SMOKE TEST, SONIC TESTS, AND PROPANE.

If no vacuum leaks are found, refer to the PC/ED for further diagnostics.
Verification of repair.
Prepare scan tool and vehicle to monitor short term fuel trims (SHRTFT's).
Get vehicle into stabilized idle condition, unless freeze frame indicates other temperatures.
Repair vacuum leak.
SHRTFTs should decrease by at least 15%. If they do not, return to Step 2.
Clear KAM and codes.
WARRANTY INFORMATION
WARRANTY STATUS: Eligible Under Provisions Of New Vehicle Limited Warranty Coverage And Emissions Warranty Coverage.

May be a front O2 issue, the wave pattern can be checked with a scanner.

But first pull the MAF sensor of and clean it with an electrical cleaner.

You need to use a smoke machine
it inject smoke into the intake help locate leaks

2001 Ford Windstar check engine code PO171 / PO174

A lean fuel condition can be caused by:

* Low fuel pressure due to a weak pump or leaky fuel pressure regulator. (Use a fuel pressure gauge to check fuel pressure at idle)

* Dirty fuel injectors. (Try cleaning the injectors)

* Vacuum leaks at the intake manifold, vacuum hose connections or throttle body. (Use a vacuum gauge to check for low intake vacuum)

* Leaky EGR valve. (Check operation of EGR valve)

* Leaky PCV Valve or hose. (Check valve and hose connections)

* Dirty or defective Mass Airflow Sensor (MAF). (Try cleaning the MAF sensor wires or filament with aerosol electronics cleaner. Do NOT use anything else to clean the sensor, and do not touch the sensor wires)

* TIP: On many Fords, a P0171 and/or P0174 Lean Code may sometimes appear because of a bad Differential Pressure Sensor (DPFE). This sensor monitors EGR flow, and is located on the engine near the EGR valve. There are two hoses that connect the sensor to the tube that runs from the exhaust manifold to the EGR valve. The sensor misreads EGR flow and the computer increases EGR which has a leaning effect on the fuel mixture. The fix is to replace the DPFE sensor.