Code PO171, PO174 Help

[cjmedina]

Remember, you still can have a bad IAC.

Do A search on troubleshooting an IAC

StreetRod can help you.

 

[2000LXS]

Will the IAC make a lean code? It is metered air

 

[2000StreetRod]

Zabteck Intake breather bypass

I just noticed that in your signature you list a Zabteck Intake breather bypass. I believe that the kit consists of a breather for the right valve cover PCV inlet port and a plug or cover for the associated port in the main intake tube.

For a normally aspirated engine I see no reason to install the device. It allows unmetered air to enter the engine via the valve cover, pass thru the crankcase, PCV valve and then enter the upper intake manifold. This results in a slightly lean condition because more air is flowing into the cylinders than is measured by the MAF sensor. Normally, the PCM can compensate for the lean mixture by reading the O2 sensors and adjusting the fuel trims. However, when the fuel trims reach a predetermined maximum the diagnostic too lean trouble code is set. The volume of air flowing thru the PCV valve is small so it has the most effect when the engine is idling. Your lean codes popping up after the filter change could just be a coincidence or the new filter could be more restrictive than the previous one.

Your 1998 should have a return fuel system. Have you performed a fuel pressure test? Clear your codes and try a cold engine start with the vacuum line to the fuel pressure regulator disconnected and plugged. That should result in max fuel pressure and a rich (rather than lean) mixture at idle.

I also suggest eliminating the Zabteck Intake breather bypass kit and returning to the stock configuration unless you can describe a good reason for keeping it.

 

[2000StreetRod]

Intake manifold vacuum lines

Since I frequently suggest checking vacuum hoses and lines I probably should try and list them. I'll start a list here and eventually generate a thread with photos identifying the listed items.

The photos below will help me list the lines.

1. top left: power brake booster

2. top center: PCV valve "T"

3. bottom center: PCV valve "T"

4. bottom left: (splits into three lines with two lines splitting again into two) fuel pressure damper, EGR vacuum regulator, evaporative emission canister purge valve, vacuum reservoir bulb below air filter enclosure

5. center: IAC valve inlet (short flexible hose and rigid tube)

6. top center: fuel vapor management valve (T connection with 7 below at front of engine)

7. bottom center: fuel vapor management valve (T connection with 6 above at front of engine)

 

[Lazzman]

Wow, tons of great information.

Streetrod, I run the Zabtech breather bypass to stop oil from flowing into the intake, my engine is old and has a lot of blow by, that extra oil gets on the spark plugs and causes a poor running condition, forcing me to Seafoam the intake a lot more than usual.

I am particularly interested that you noticed this mod because I recently had my vehicle inpsected and when I do that- the (breather bypass being illegal) I replace it with the regular stock hose. Problem occured about a day after I switched back breather bypass. Funny thing though it does not make a difference with the idleing but it seems to have this time. Maybe it is because I disconnected the battery when I re-installed the Bypass Breather?

Also, how can unmetered air get into the intake through the Bypass hose in the valve cover? Wouldn't that air already be passed the intake?

Is it possible the IAC could be the culprit here? Mine is about three years old.

Thanks for all the expert advice.

 

[2000StreetRod]

Stock PCV flow path

The stock air flow path for ventilating the crankcase is as follows:

1. Thru air filter into main intake tube
2. Out of main intake tube thru hose into right valve cover
3. From above right head into and throughout crankcase
4. Out of crankcase thru the breather/screen to PCV valve
5. Thru PCV valve into "T" then to left and right ports on upper intake manifold

Since the absolute pressure at the intake manifold ports is less than the absolute pressure in the main intake tube air always flows in the same direction unless the PCV valve (one way check valve) or breather/screen is blocked/clogged.

When you replace the hose from the main intake tube to the right valve cover with a breather then atmospheric air enters the crankcase that has not passed thru the MAF sensor. It's no different than having a leaking vacuum tube. If you have crankcase fumes exiting from your Zabtech breather then it probably means your PCV valve or crankcase breather is clogged.

Since you only have closed throttle problems you could have a bad IAC valve. The PCM normally does not detect a defective IAC valve. You might try sticking a spacer (such as a dime) between the throttle stop adjusting screw and the throttle stop. If it starts better then your IAC valve may need replacing.

 

[Lazzman]

Thanks for the detailed answer. I will give it a try with the IAC valve.

 

[Lazzman]

Tried reconnecting the PCV breather tube and reset the computer. Truck ran good for about 30 miles then the light came back on.

I am thinking it could be the TPS but am getting frustrated because I have replaced just about all of the things it could have been without any results.

So far I have:

*replaced the MAF with a new one
*Cleaned the IAC
*Checked all Vac hoses for connection
*Checked & cleaned EGR Valve
*Replaced PCV valve
*Replaced fuel vapor management valve
*reinstalled PCV breather hose

Still get a high idle when warm all of the time, at rare times idle drops so low it almost stalls the vehicle, Still gettting banks 1 & 2 lean codes. Idle goes crazy sometimes and slowly revs all the way up when I put it in park, I have to shut off the engine to keep it from taching out.

If it is the IAC Valve why the lean codes from the computer, would that even send a lean code?

I am thinking of tackling the upper and lower intake gaskets unless I can come up with a better idea. I am not sure where to go next, Idle air valve and TPS seem logical but would either one of them through the PO174 & 174 codes????

Any help is greatly appreciated, this is driving me and me wallet crazy

 

[2000StreetRod]

max rev

. . . Still get a high idle when warm all of the time, at rare times idle drops so low it almost stalls the vehicle, Still gettting banks 1 & 2 lean codes. Idle goes crazy sometimes and slowly revs all the way up when I put it in park, I have to shut off the engine to keep it from taching out.

If it is the IAC Valve why the lean codes from the computer, would that even send a lean code? . . .

High revs require intake air flow. I guess its possible if the TPS outputs an erroneous high voltage the PCM may try to match the requested engine speed by adjusting the IAC valve but that seems unlikely. I suggest that you test the TPS: TPS Test Procedure

Then I would make sure that the throttle plate is closing fully when you release the accelerator. Have you performed the zip tie throttle cable mod? Some members don't leave any slack in the cable at closed throttle which can cause the throttle plate to remain open when the accelerator is released.

I suspect that your IAC valve is erratic and needs replacement.

 

[Lazzman]

I do have the zip tie mod but it was put on a couple years ago with no trouble.


I am sure the IAC has something to do with the idle but would it throw the codes that I am getting? That does not make sense to me, unless there are many problems going on.

I appreciate the advice Street :biggthump

 

[2000StreetRod]

Idle adjustment procedure

I suggest that you perform my Idle adjustment procedure and then try running with the IAC valve electrical connector disconnected. The PCM will report a DTC that the IAC valve reading is out of range. If your problems and lean codes go away then you can be fairly confident that your IAC valve is bad.

 

[Lazzman]

Will do, by the way I am short on cash can you suggest a good brand of IAC for short money? I am running out of money trying to chase this problem down.

Thanks

 

[2000StreetRod]

IAC valve source

Will do, by the way I am short on cash can you suggest a good brand of IAC for short money? I am running out of money trying to chase this problem down.

Thanks

When I was trying to solve my coldstart flare problems I bought one from Advance Auto because I was in a hurry to see if that solved my problem. I didn't take the time to compare pricing. The unit worked fine and I'm still using it. Turned out my problem was leaking intake manifold gaskets so now I have a backup unit. If you perform the idle adjustment you may be able to run for a while without an IAC valve as long as you prevent the A/C compressor from being activated. You could disconnect the electrical connector at the bottom of the compressor.

 

[Lazzman]

Performed many tests today with no real clues present.

First I tested the fuel pressure at idle it was 40psi with the fuel regulator connected, I did this when the vehicle was cold and when the engine was sputtering and wanted to stall the fuel pressure rose to 45 psi which seems odd to me. I have a 1998 with a returnless low pressure system. Those fuel readings seem about right.

Next I tried to perform the setting of the idle as descirbed in Streets link. After the vehicle was warm I disconected the IAC and the idle dropped to about 525 and held there steady, no need to adjust this. When I plugged it back in the idle went back to 750rpm or so.

Next I unplugged the TPS the engine immeadiatley hiccuped and started to try and find a smooth idle which it eventually did. When I plugged the TPS back in the engine returned to normal.

From my tests I can assume that the fuel pressure is good and fuel filter was installed correctly, the TPS is working fine as is the IAC.

So where do I go from here? I should mention I am using about 10 or so ounces of coolant every 200mi and it does not seem to be leaking out on the ground, nor is it in the oil or exhaust.

I don't know what else could be left to check?

 

[2000StreetRod]

invalid TPS test

. . . First I tested the fuel pressure at idle it was 40psi with the fuel regulator connected, I did this when the vehicle was cold and when the engine was sputtering and wanted to stall the fuel pressure rose to 45 psi which seems odd to me. I have a 1998 with a returnless low pressure system. Those fuel readings seem about right.

I believe that you have a return fuel system. Ford switched to the returnless fuel system in 1999. When the engine was sputtering your vacuum was probably fluctuating which would cause the fuel pressure regulator to vary the fuel pressure. Your fuel pressure is about right for a return fuel system. It would be low for a returnless fuel system (>60 psi for any engine speed). See my thread: Fuel pressure test procedure

Next I tried to perform the setting of the idle as descirbed in Streets link. After the vehicle was warm I disconected the IAC and the idle dropped to about 525 and held there steady, no need to adjust this. When I plugged it back in the idle went back to 750rpm or so.

Sounds like the idle adjustment stop is correct and the IAC valve worked when reconnected.

Next I unplugged the TPS the engine immeadiatley hiccuped and started to try and find a smooth idle which it eventually did. When I plugged the TPS back in the engine returned to normal.

That was not a test of the TPS. All you did was check the PCM determined invalid TPS value and closed throttle value. You need to monitor the voltage change with the ignition On and engine Off throughout the range from closed throttle to WOT looking for dropouts or erratic readings.

. . .
So where do I go from here? I should mention I am using about 10 or so ounces of coolant every 200mi and it does not seem to be leaking out on the ground, nor is it in the oil or exhaust.

I don't know what else could be left to check?

So for this test session the engine sputtered for cold start but ran fine after warmup. You said that you had your engine coolant temperature (ECT) sensor replaced two years ago. Are you sure it wasn't the engine temperature sender that drives the temperature gauge on the instrument panel? Your cold start symptoms sound like those for a defective ECT sensor. Did you actually test it with an ohmmeter? Are you sure that the electrical connector to it is making good contact? Both wires (light green/red and gray/red) have to make a good connection because the return (gray/red) is not grounded.

However, a bad ECT sensor cannot cause the engine revving to near redline as you mentioned in an ealier post. That can only result from airflow (stuck open throttle plate, wide open IAC valve, busted or disconnected vacuum hose, cracked intake manifold or leaking gaskets.

I just remembered that some of the 1997 and 1998 SOHC V6s have a PCM controlled variable intake system (VIS). The length of the intake runners changes around 3,000 rpm. There is a vacuum line to a solenoid activated vacuum switch. The switch output goes to a vacuum motor that is mechanically linked to a lever control of the intake runners. There is an intake manifold mounted vacuum reservoir associated with the system. Do you have VIS? If so, have you checked its associated vacuum connections/lines?

 

[Lazzman]

yes, it was the coolant temp sensor that was replaced because the mechanic who was testing it, was using a new engine monitoring software and said that the ECT was not working properly.

Don't know what brand he put in but it is possible that it is failing again. I would have no problem replacing it, as I was prepared to spend the moneuy and time replacing the IAC and TPS.

Sorry, I did not mention that I checked the TB and it is closing properly with no obstructions.

I am very familiar with the VIS valve and had it replaced a couple years back it is connected properly.

When I was trying to figure out a problem, which eventually turned out to be a broken timing chain tensioner, I replaced a lot of the Electrical components.

One more interesting thing- When I am cruising on the highway turning about 2500rpm at 70mph I will take my foot off the accelerator and it will take the engine about 3 seconds to respond, before the tach drops down and vehicle stops moving forward. This seems odd as it should happen immeadiatley, another reason why I kinda think the TPS is failing. I have always had trouble testing the TPS and even mashed the wires trying to get the probes in. For me its easier to just buy a new one.

Dale, thanks again for helping with this issue, its driving me nuts.

 

[Lazzman]

So where to now? I am leaning toward putting in new upper/ lower intake gaskets.

For clarity here are the problems I am experiencing.

*Code PO 171 & PO174, I have disconnected the battery each time I do something to solve the problem but the code always comes back.

*When engine is cold it will not idle, idle drops down and almost stalls but does not, just sputters around 500rpm.

*When engine is warm idle will be higher than normal 850 in drive, 1100 in Park.

*idle will flare at times when the truck is warm, but never when cold.

I happen to be broke at the moment and have spent about $300 so far trying to fix this problem to no avail. Need help and advice before I blow all of my savings

Any sure way to know if it is the intake gaskets?

Puzzling to me because at cold start up the idle dies way down, it does not go up like in the usual bad intake gasket fashion.

Thank you

 

[Lazzman]

If it is bad upper and lower intake gaskets, what symptoms would I have? I already have the lean codes in both banks and a higher than normal idle.

How long does it take to change the gaskets, do I need any special tools?

Thanks

 

[scucci]

http://www.fordforumsonline.com/for...0-ford-explorer-sport-misfiring-when-hot.html

Read the 00m12 tsb attachment for the procedure to r&r the intake manifold gaskets.

 

[Lazzman]

Thanks Scucci- Great Info :biggthump