Contour Enthusiasts Group Archives Forums General Troubleshooting CEL w/ P0171 code, Stalling.

I'm getting the P0171 error code on my 98 GL Sport, 4 cyl, auto. With the rough idle, crappy gas mileage, and hesitation. The rough idle is only when the engine is cold like the in morning or after it has sat for a few hours. I pulled the code and cleared it from the system so the CEL would go out.

I read the forum on this error seems like a lot of people are getting this error code. I could not find any vacuum leaks, but I did take the electronics out of the MAF and they had all kinds of black crud on them. I cleaned the MAF electronics with CRC Electronics Cleaner. Now when I drive the car it will just stall out. Bad part about it is that whatever is screwed is not giving any codes.

The engine will stall when you let off the throttle after light acceleration, if you ease out of the throttle it does not stall, but this does not happen all the time.

Anyone have any ideas? Bad MAF?

Things I have done, Replaced plugs/wires(Ford), Replaced upper and lower O2 sensors(Ford). It has 100K miles on it.


Thanks, Sorry for the long post.

Are you sure there is only one CEL code being thrown? Sometimes there is more than one CEL stored in memory.

If you haven't seen it before, the following is from the Ford TSP:

Diagnostic Trouble Codes (DTCs) P0171 bank (1) (cylinder #1) and DTC P0174 bank (2) indicate the fuel/air ratio is too lean. The fuel adaptive system is at the rich correction limit.

DTC P0172 bank (1) and DTC P0175 bank (2) indicate the fuel/air ratio is too rich. The fuel adaptive syste is at the lean correction limit.

DTCs HO2S Reference list:

-- HO2S-11 = DTCs P0171 and P0172

-- HO2S-21 = DTCs P0174 and P0175

Possible causes:

Fuel system
-- Excessive fuel pressure.
-- Leaking fuel injector(s).
-- Leaking fuel pressure regulator.
-- Low fuel pressure.
-- Contaminated injector(s)

Induction system
-- Air leaks after the MAF.
-- Vacuum leaks.
-- Restricted air inlet.
-- PCV system.
-- Fuel purge system.
-- Improperly seated dip stick.

EGR
-- leaking gasket.
-- Stuck open EGR valve.
-- Leaking diaphragm.

Base engine
-- Oil overfill.
-- Cam timing.
-- Cylinder compression.
-- Exhaust leaks before or near the HO2S's.

* Check air intake for leaks, obstructions and damage.
* Check air filter, air filter housing for blockage.
* Verify integrity of the PCV system.
* Check for vacuum leaks.

On the V6 this is a typical code you get when the upstream O2 sensors are dying. As they get weak, they start reading lean. The computer richens up the mixture to try to correct resulting in decreased fuel mileage.

I replaced both the up stream O2 and the down stream O2, it didn't make any difference. When I was reading the forum I saw that a few people fixed this problem buy cleaning the MAF, so thats what I did. After the cleaning the stalling started, but the crazy idle, and hesitation are gone.

The stalling doesn't happen all the time, like today I drove the car all the way to work using surface streets and the highway (40+ miles) and it never stalled.

Could it be that the ECM is still learning the MAF signals since the MAF was giving the wrong info for so long?

Thanks

It is probably an air leak somewhere.. Correct me if I am wrong, but wouldn't a vacuum leak cause stalling after hard acceleration then backing off? Just a thought, probably wrong lol

Cleaning the MAF sensor does not mean it is working properly. You may need to do more in depth diagnostics.

If you do replace the MAS, I just ordered one from fordpartsonline.com and they were half of what the dealership wanted.

Just fyi.

We have been fighting the EXACT same problem for months now. Dies just off idle from a stop, also same error code. We also replaced both O2 sensors on a trip last year, but it at that time, we didn't have the stalling problems. The CEL came on and our gas milage dropped to about 6mpg, so I knew it was the 02 sensors. After replacing them, it ran fine till summer this year.

Replacing the fuel pump & filter helped reduce the stalling program quite abit, but it was still there (1-2 times per week it'll stall.) Also replaced the TPS, but it had no effect. I bumped the idle up slightly and it helped. The reason I did that was that at idle with the lights on and AC on, the voltage would drop to 11.2V. I was thinking the computer was getting a low reading from the TPS, and so that's why it was stalling. After slightly bumping the idle the voltage went to 12.8 at idle and 13.2V all the time. It did seem to help, but it was still there.

So today I cleaned the MAS and Throttle body and it's sure running better. Only time will tell if the stalling is fixed or not. (see my other post today.)

We also have 100K on our car. It's a 4 cylinder automatic.

It sounds way more difficult than it actually is. Change the upper and lower intake manifold gaskets. The way FORD designed these gaskets does not make sense and they easily become a source of headaches for us as owners. I had the same code as well as the P03006 code and I tried everything from the ignition system to th fuel system and finally decided to tear apart the top half. Right away I could see the problem (and the design flaw of the gaskets) and my car runs just like it should. The nice part about this is that it cost me less than 100.00 to fix it. (after spending almost 500.00 to not fix a thing.) Give it a shot, it's cheap and you'll end up doing it sometime anyways.

If you clear the codes, when the engine dies does it through a code for you? Thats the most frustrating thing to me is that the stalling started but with no error codes. Something is wrong if the car stalls kinda lame that the ECM dosent think so.

Not sure what else to check out. Guess I'll drive it for awhile and see if the stalling stays around.

The MAF sensor is delicate and the exact position in the housing is critical, many people have damaged them. Then again yours has seen a lot of use, they get slow to respond sometimes and cause wierd problems.
Cleaning it may have uncovered annother problem and its about time you cleaned the EGR, TB, intake, IAC, and checked the PCV system if you have not done so.