Ford Windstar - fixing PO171 and PO174

dmdkanadmdkana Member Posts: 1
How do I fix the codes PO171 and PO174?

All I know is that my fuel is lean on both banks.


  • autodrautodr Member Posts: 27
    WOW... is that a really wide open question or what... I know you think you're asking a simple question, but "lean" and "rich" codes have the longest possible causes list of ANY of the fault codes.

    The conditions under which it is lean can be used to steer the diagnostic direction. When those codes set, there was also some "freeze frame" data that went with one of them. Now, maybe the tool being used won't show it to you, depending on the quality of the tool. But that FF data is helpful.

    A lean condition at idle only, and not higher RPMs is a possible indication of a vacuum leak.

    A lean condition at higher RPMs but not at idle is an indication of a fuel delivery problem like pump and filter.

    A lean condition at idle that suddenly swings to a rich condition at higher RPMs is an indication of a contaminated MAF sensor.

    However, it it extremely common for the plastic upper intake seals to leak vacuum. It is also very common for the IMRC shaft seals in the lower intake to leak vacuum. The upper seals aren't that big of a deal, but the IMRC shaft seals in the lower require a complete new lower intake manifold (the actual aluminum manifold) to correct.

    Ford also has a reprogramming (reflash) that helps. Often, a new set of upper seals plus the reflash will "hide" the IMRC shaft seal leakage. But eventually the lower manifold gets do worn out that the reflash won't hide it and you'll need a new lower intake manifold.

    That is just one common issue may not be your problem. You will need to take the vehicle to a shop that can monitor fuel trim PIDs on the scan tool. They can spray the intake seals and watch the reaction in the trim PIDs to determine any vacuum leak.

    Another common issue is when someone replaces the air filter, and the plastic PCV hose pulls out of the snorkel on the back side (nearest the master cylinder)... that causes a lean code at idle due to unmetered air entering the engine.

    I'd check that PCV hose first and if that is ok, take it to a shop. Also, the PCV hose that goes to the PCV valve (in front).... make sure oil hasn't gotten to the rubber part where it slides onto the intake, swollen it and causing it to leak vacuum. Those are a couple of DIY'r repairs I can think of... the rest really need a tech with proper test equipment to figure out.
  • fordowner4fordowner4 Member Posts: 1
    Chances are that you have the same problem than most of us in this case: upper and lower plenum gaskets for the intake manifold. You can even look the procedure up online it's so common for Windstars.
  • diclemegdiclemeg Member Posts: 10
    hopefully autodr or anyone with great knowledge can assist.

    i have a 2003 with 43,000 miles, and the problem im having is high idle but no error codes and i cannot find leak. When I start cold, it runs 1600-1900 rpm initially, and then drops to 900 like its supposed to, but will only stay there a few seconds, then it'll ramp up to 1100 or so. At this point, if I put it in drive, it'll take off on its own with touching the pedal, and the rpms will slowly rise including the vehicles speed, and will get to 20mph sometimes. Any driving during this period before its fully warm (which takes 15 minutes) and its as if it'll coast forever, and I'm using the brake instead of the accelerator. It seems like its 200 to 300 rpm higher than it should be. When the engine is fully warm, at a stop it'll be at 800rpm, but if I put into neutral at this point, it'll come up to 950rpm. Its driveable, however, its very annoying and is not pleasant driving short trips.
    Ive replaced the IAC valve, throttle sensor, cleaned MAF, throttle body, cable, and tried to find any leak but am coming up short. Note that I am not getting any error codes, stored or unstored. Please assist.
  • autodrautodr Member Posts: 27
    Disconnect the battery for a few minutes. Reconnect, drive it and see if that seems to fix it. If it does, test the battery.

    What kind of vehicle? I'm assuming something in the Ford line.
  • diclemegdiclemeg Member Posts: 10
    yes, a 2003 ford windstar
  • diclemegdiclemeg Member Posts: 10
    I finally attached a scan tool.. .... and here is what i found..... .the "absolute throttle position" reads at 18.4% without touching the pedal, and goes up from 18.4 if I do touch the pedal. If I disconnect it, it reads 0%. The short and long fuel trims were -1% and 3% and varied but never got above 6%...

    recall that i already changed the TPS sensor a week ago.
    calling all experts, please advise here.
  • autodrautodr Member Posts: 27
    Does your scan tool give you the TPS in volts also? Or is it only generic scan data.

    If your scanner won't give you the voltage, use a DVOM directly at the sensor and measure voltage on he signal wire and the ground. There should be no voltage on the ground wire. TPS voltage should be around .8 If the signal voltage is higher than that with no voltage on the ground, inspect the throttle plate stop screw... maybe someone adjusted it up. If not, then suspect the wrong TPS or a poorly made one. If the voltage is correct with the absolute TPS value reading that high, disconnect the battery... reconnect after a minute, and see if the absolute TPS is now correct at zero. If it is, test the battery,
  • diclemegdiclemeg Member Posts: 10
    Hi autodr,
    the scan tool does not have volts. however, get this.. when the tps sensor is attached to the throttle housing, it actually has to open and turn a little bit, which is causing the 18.4% reading. i know this because i took it off with the computer in front of me and it went to zero. then i put it on half way and it read zero and in order to seat the screws, i had to turn it to the point that it read the 18%. The flat plastic knob that is attached to the throttle plate and what turns the tps sensor at closed position is not at 0 degrees like this " -- " but titled downward like this " \ " (but not that exagerrated). I guess the question is whether the pcm knows that the downward tilt is absolute zero and accounts for it.
  • autodrautodr Member Posts: 27
    Absolute throttle position is NOT a measured position. It is a learned or calculated position. It is the position that is in reference to the lowest measured TPS voltage. You need to know the measured voltage. That phantom 18% may be coming from an incorrectly learned closed TPS position. If you have a volt meter, try measuring the vltage at the TPS and let me know what you read. There are 3 wires there, One is a 5 volt reference, one is a a ground which will only have a couple millivolts on it... and the other is your signal wire. It will start around .8 volts closed and raise up to about 4.8 at wide open throttle.

    You have only generic level scan access then.... which is better than nothing at all. But, you have to remember that you are not seeing "actual" TPS position on that scanner... you are seeing more of a "virtual" TPS position. The position displayed is relative to the lowest measured voltage that the PCM saw.

    You can also try disconnecting the battery for several minutes then reconnect. That will clear out the lowest measured TPS voltage from the PCM's memory. And unless the TPS is at a ridiculous high level... like more than a volt, it should accept that first key-on TPS voltage as the new "closed" TPS voltage.

    It may be that the TPS they gave you is the wrong one. I'm assuming you went to a part's store rather than the dealer, which doomed you to get the wrong one early on. At the part's store, they ask you year. make, model, and engine and hand you the only one they list for it because they do a "one size fits most" thing. Whereas there may be 2 or 3 different ones for that vehicle depending on the vehicle's calibration code which the dealer will use to get the correct one.

    However, some TPS's are under slight tension when installed so that test you gave may or may not prove anything. I really would like the voltage to get a better idea of where that TPS is sitting at at closed throttle position.

    Another quick test here would be to unplug the IAC valve. If the engine idles down to the point of near stall, or does stall, then it is likely that the phantom TPS position is the only problem. When the PCM sees the TPS open, it cranks the IAC open to anticipate "dashpot" mode when you let off of the gas.
  • gregwrench63gregwrench63 Member Posts: 3
    I have three MIL codes , 2 lean banks and a EGR flow code . I replaced the EGR and EGR flow sensor . Then , I found that the linkages to both IMRC 's had fallen off . I need to know 2 things , 1) does anyone know where to get the linkages and retainers besides from Ford and ,2) could this be throwing lean codes ? I am assuming that the rough idle is associated with the IMRC being inop . It acts sort of like a vacuum leak but I cannot find one and that is what is leading my this way . Help and thank you.
  • autodrautodr Member Posts: 27
    The little white plastic bushings are available at the dealer for about 7 dollars each.

    If a linkage is missing, then you are in big trouble. The linkages are not available separate and do not come with a new IMRC unit. In order to get new linkages you have to buy an entire lower intake manifold... but the lower intake manifold might be your source of your lean codes anyway because the IMRC shafts leak vacuum there anyhow and the seal in the shaft that leaks is not availble without buying a lower intake manifold anyway.

    I keep the old IMRC linkages when I replace a lower intake because I know you have to buy a 3 hundred and something dollar lower intake to get them. It is likely that a tech at a local Ford dealer near you will have a few in his tool box too for the same reason.

    Lean fault codes have the largest list of possible causes out of all of the fault codes, second only to rich codes. That engine has a few intake leakage sources, like the upper intake seals and bolts, pcv valve lines, and lower intake IMRC shaft seals are all common causes, but other possibilities are possible. It should be checked out by a qualified tech. Otherwise, you might through a LOT of expensive parts at it attempting to fix it. Paying to properly diag the problem and fix it right the first time is cheaper than guessing.

    BTW... there is also a reflash for the PCM that "hides" much of the vacuum leakages. It doesn't fix the cause, but helps cover it up and might keep the light out. If you take it to a dealer, you might find it can be fixed with only a reflash.
  • gregwrench63gregwrench63 Member Posts: 3
    I want to thank autodr for the great suggestions with respect to my IMRC misery . I did however , find a way to beat Ford at it's own game by manufacturing new linkages from 4mm welding rod . I did use new bushings but , instead of Ford linkage , I bent "Z" bar style linkages and they are not falling out any time soon . I was unaware that the IMRC rods leaked vacuum. How much , roughly , does an intake manifold cost ? The replacement looks fairly straightforward .
  • autodrautodr Member Posts: 27
    *prices may vary :)

    The last time I had to get one (a year + ago) I seem to remember $365.00 as the price. Plus the gaskets.
  • gregwrench63gregwrench63 Member Posts: 3
    I'm hoping not to have to go that route . We have an account with a local Ford dealership and so far the consensus of thier techs is the upper and lower plenum gaskets with the upgraded bolt kit . Luckily , I get them at jobber rate .I'll let you know how that all shakes out. But I do appreciate all the info you gave me . Thanks again.
  • autodrautodr Member Posts: 27
    The upper intake seals and bolts... plus the reflash to hide the leaking IMRC shafts fix about 95% of them... its that last 5% that actually require a new lower intake.

    I'd say that for every 10 I see, 1 needs a lower intake.
  • kakujiaatkakujiaat Member Posts: 2
    autodr your post is very precise.i have same codes and i changed gaskets and van runs good.only problem it gets into is when it idle for 8 to 9 minuts it loos it,s synchronization and idle rough and cut off.

    secondly if i leave vehicle hot and return after 5 to 12 minutes it idle rough,but if i let it cool little more then it starts ok.

    in traffic for 5 to 8 minutes and it get to same rough idle and loss power on changing to higher gear atleast pull through
    i drove nearly 7000 miles in this condition after changing gaskets
    thank you for respons
  • kakujiaatkakujiaat Member Posts: 2
    i wish autodr or someone please shed some lights on my post #17 for any solution possible
  • gec19deltagec19delta Member Posts: 1

    A Ford P0171 is a LEAN code fpr cylinder bank 1, and P0174 is a LEAN code for cylinder bank 2. These codes commonly occur on many Ford vehicles, and are set when the powertrain control module (PCM) sees the air/fuel mixture is running too lean (too much air, not enough fuel).

    When the Check Engine Light comes on, either one of these codes, or both, may be found when a code reader or scan tool is plugged into the vehicle diagnostic connector. IF the vehicle is driven long enough, typically both codes will be set.

    A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive.

    A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transverse-mounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2).


    A lean fuel condition may exist if the engine is sucking in too much air and/or the fuel system is not delivering enough fuel. If bad enough, a lean fuel condition may cause lean misfire, a rough idle, hesitation or stumble when accelerating, and/or poor engine performance.

    Unmetered air can enter the engine through a vacuum leak, a dirty airflow sensor that is not reading airflow accurately, an EGR valve is not closing and is leaking exhaust into the intake manifold, an EGR valve that is allowing too much flow (because the EGR differential pressure sensor that monitors EGR flow is faulty and is under-reporting EGR flow).

    If the problem is not enough fuel, the underling cause may be a weak fuel pump, restricted fuel filter, leaky fuel pressure regulator or dirty fuel injectors.


    One of the most common causes of Ford P0171 and P0174 lean codes is a dirty mass airflow (MAF) sensor. The MAF sensor is located in the air inlet tube
    just ahead of the throttle body. The MAF sensor should be protected from outside dust and debris by the air filter, but sometimes the air filter doesn't fit real tight inside the housing and allows unfiltered air into the engine. Dirt can stick to the MAF sensor wire and form a coating that slows the response of the sensor to changes in airflow. The MAF sensor can also be contaminated by fuel vapors that back up through the intake manifold and throttle body when the engine is shut off. The vapors can leave a waxy coating on the sensor wire. This causes the MAF sensor to under report airflow, which in turn misleads the powertrain control module (PCM) so it doesn't add enough fuel to maintain a properly balanced air/fuel ratio. As a result, the engine runs lean and sets a P0171 and/or P0174 code (see Ford TSB 98-23-10 for details).

    If the MAF is dirty, the fix is easy enough: just clean or replace the MAF sensor. In many instances, the MAF sensor can be successfully cleaned by spraying the sensor element with electronics cleaner. Do not use any other type of cleaner as this may damage the sensor.

    Disconnect the air inlet tube just ahead of the sensor, and then spray the electronics cleaner through the screen at the wire element in the center of the little MAF sensor. Let the cleaner soak in for several minutes, then give it another shot of cleaner. Let it sit another five minutes, then reconnect the air inlet tubing and start the engine.

    If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem.


    Another common cause of Ford P0171 and P0174 ean codes is an engine vacuum leak. Ford TSB 04-17-4 details procedures for checking fuel trim and looking for vacuum leaks.

    On 3.8L Fords with a split-plenum intake manifold, the port gaskets and isolator bolt assemblies for the upper plenum can deteriorate over time and leak air, often as a result of oil being sucked into the intake manifold through the PCV system. Also the vacuum hose that connects the fuel pressure regulator to the intake manifold can swell and leak vacuum where the hose connects to the manifold. Ford TSB 03-16-1 says the fix involves several steps: remove the upper manifold plenum and replace the original gaskets and bolts with revised ones, replace the front valve cover with a revised valve cover that reduces the amount of oil vapor sucked into the PCV system, inspect and replace the fuel pressure regulator hose, and finally, reflash the PCM so it is less sensitive to lean fuel conditions.


    Ford p0171 AND p0174 lean codes can also be set by a bad EGR differential pressure sensor. These sensors have a very high failure rate once a vehicle has more than about 60,000 miles on the odometer or is more than five or six years old.

    The DPFE sensor is mounted on the engine, and is attached with two rubber hoses to the tube that routes exhaust gas to the EGR valve. The original equipment sensor has an rectangular aluminum housing about three inches long. Corrosion inside the sensor reduces its sensitivity to EGR flow, causing it to under-report EGR flow. The PCM responds by increasing EGR flow, which may keep the EGR valve open longer than usual creating a lean condition in the engine. Thus, a bad sensor may set a P0401 code (insufficient EGR flow), or it may not set an EGR code but a P0171 and/or P0174 lean code instead.

    The cause of the P0401 code in most cases turns out to be a bad DPFE sensor, not an EGR valve problem or an EGR valve that is plugged up with carbon (though this can also set a P0401 code). An aftermarket replacement DPFE sensor costs less than $50 and usually gets rid of not only the P0401 code, but also the P0171 and P0174 codes, too.

    good luck god bless
  • autodrautodr Member Posts: 27
    Good write up. Just a few details I'd like to add or change.

    "A P0171 lean code for bank 1 is the cylinder bank on the RIGHT (passenger) side of the engine on Ford vehicles with a V6 or V8 engine and rear-wheel drive.

    A P0174 lean code for bank 2 is the cylinder bank on the LEFT (driver) side of the engine on Ford vehicles with a transverse-mounted V6 engine and front-wheel drive. This code is not set on four cylinder engines (no bank 2)."

    Right/Passenger/Rear... depending on longitudinally mounted (rwd) or transverse mounted (fwd)

    LEFT/Driver's/Front... depending on mounting.

    "One of the most common causes of Ford P0171 and P0174 lean codes is a dirty mass airflow (MAF) sensor."

    "one of" I agree... but probably the most common is a vacuum leak.

    "If the lean codes keep coming back, the MAF sensor may have to be replaced if the engine does not have a vacuum leak or fuel delivery problem."

    Careful. What would happen if it had E85 added to the tank? What if someone damaged the inlet screen to the MAF (not sold with a MAF unless you get the entire air cleaner housing). I've also seen some really P-Poor quality air filters (especially go-fast types) cause rich and lean codes because the nose cone is shaped wrong causing a distorted air flow shape through the MAF sensor. No part should be replaced based on the reoccurred of a code because codes don't mean "replace this" or "this part is bad". In the case of a lean or rich code, fuel trim characteristics should be observed, plus BARO reading PID, and/or volumetric efficiency calculations should be made to peg a bad MAF. One common characteristic of a faulty MAF is that the Load% PID and the LTFT PID will follow each other perfectly when graphed out.

    All of the Ford Plastic intake manifolds have seal issues. I know that old TSB may only mention one style. But a lot has happened since then. Also, on Wind-ed Stars, the lower intake also leaks. Not mentioned in the TSB. The IMRC shaft seals leak vacuum. FoMoCo released a reflash that hides the leak so they didn't have to eat many under warranty. But eventually they leak bad enough there that the lower intake manifold also has to be replaced because they leak beyond what the new software can hide... the actual aluminum manifold.

    As for the 4cyl engine not having a bank2.... as long as you are talking FoMoCo, then you are right. No FoMoCo 4cyl that I know of... yet... have a bank 2. But, a 4 cylinder in-line engine can have a Bank2. Just look at about a 2002 Nissan Sentra. Cyls 1 and 2 are piped to the B1S1 O2, and the #3 and #4 cyls are piped to the B2S1 O2. Then they have 2 separate Cats (inside a common housing), with a B1S2 cat monitor, and a B2S2 cat monitor. A total of 4 O2 sensors with a bank 1 and bank 2 on an inline 4cyl engine. They are out there :) Just not in the FoMoCO world.... so you are still in the right.
  • troundatrounda Member Posts: 5
    i pulled the transmission and replaced torque converter and front seal drove down the road 0/d light started flashing getting this code p1744 please help need this van so my mom can go to work
  • bigredrasabigredrasa Member Posts: 1
    edited January 2011
    In the good/bad old days, carburetor icing could cause driveability problems in cold, damp weather. We have had very cold and damp weather in the last month, and I've had the P171 & P174 codes come on twice. After resetting, they stay off for some time. Could ice build up on the MAF Sensor cause the codes? It could explain why they come on only in very cold and damp weather.
  • kc9kpqkc9kpq Member Posts: 1
    New to this forum.I have a 02 windstar. I replaced the isolator bolts gaskets imrc bushings valve stem seals (bank 2 only) valve cover fuel pressure vac line and pcv + vac line. dorman kit 615-177 and still getting the code for bank 2. I was getting bank 1 and 2 before all this. . Odes any body recommend the DPFE, mine is not the metal one mounted near the fuel rail. it is plastic and mounted with short hoses about midway between the egr valve and radiator. also I wonder if I should reflash the pcm (not really happy about Ford charging 100 dollars to fix thier mistake)

    Thanks in advance
  • billyzekebillyzeke Member Posts: 1
    OK i had these problems since i bought the piece of [non-permissible content removed] a year ago ! both codes came up when inspected thought i lost papers where i wrote them down but found em ! Was told two sensors were bad and EGR valve ! Problems are bad MPG city maybe 11 MPG surges and kicks when stop at light stalls after idling too long etc... :( I reset the CE light by disconnecting battery van ran far better after that but of course CE light comes back on after about 15 - 20 mins driving ! :cry:

    SAW the last answer and i agree has to be in the exhaust or air intake thingy I did spot crack in housing fixed it , and it didnt close too good ! Also fixed that ! I also presume a vacumm leak some where is the problem ! :confuse:
    SO after i fix or cannot find a vacumm leak or it's not the air filter housing what do i need to replace That MAF thing or The EGR valve and that too ? I get good used parts at yard where you pull it off maybe cost $15 - $35 tops ! IF they don't work then i go good ol pep boys and get the best priced ones ! I need this van to go another year because I make money with it ! It has 198,000 on it right now only major problem i had was starter went kaput when coming out of Home depot LOL Got it started by rocking van and turning key ! BUT next day wouldnt start 2nd time and had to tow it in total cost lifetime starter $340

    Has other wacko problems electrical but somehow they just start working right again ! THIS is MY last FORD product ever ! Had EM all Mercury Lincolns etc .. each one lived up to it's name FIXED OR REPAIRED DAILY back words DRIVER RETURNS ON FOOT ! LOL
  • kendermokendermo Member Posts: 1
    DIRTY MAF SENSOR fixed my errors. It's easy and cheap, try it first. Buy a can of MAF cleaner, spray it on. Hardest part is loosening the darned gigantic air filter and reconnecting it (this used to be so easy!) Broke 2 fingernails doing this and got my hands dirty. I hate this vehicle!! Simple things are such a pain on it.
  • gman366gman366 Member Posts: 1
    I have a 2002 Windstar van with a V-6 engine. I just had my radiator flushed & filled, and the service man found a large quantity of oil in the water. He flushed it , but there is still a lot of oil in the water.
    I had put some radiator flush in the day before. I also had my oil changed the week before in a quick-change place. Could a helper have put oil in the radiator filler tank by mistake?

    #1. What could cause this? My crankcase & trans oil levels are normal.

    #2. What should I do about it?

    #3. Is my oil cooler air or water cooled?
  • realtechautorealtechauto Member Posts: 1
    So i did and intake manifold gasket, thermostat, battery, egr, 6 injectors, plugs, wires, coil, high flow air filter, pcv, cleaned everything( removed all carbon i could get too), coolant temp sensor. put it all back together and it runs with a bit of a rough idler. rev it up and it runs smooth. at idle and under acceleration(in neutral) under 3000 rpm, it bangs in the exhaust(backfiring). removed the exhaust from manifolds, still did and and shot fire balls. i disconnected number 4 and 6 fuel injector connectors, the banging went away. the vehicle ran nice in neutral(injectors were reading about 12 ohms). i rev the engine up to about 3500 or more and the banging stop and i have crazy power in the power band. so all of this is going on and i have run the vehicle for at least an hour and have started and shutoff the vehicle numerous times, but my MIL STATUS is OFF. Do you think i need to reprogram the PCM or is it possible my timing jumped. when i saw the vehicle it had all kinds of codes and only ran on 4 of 6 cyl. and a noise under heavy accelerations(rattling valves kinda noise). i need to know if i should try and reprogram the pcm or spend 7 hours of my time just to check alignment marks... Thank you for your time
Sign In or Register to comment.