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1998 Mercury Mystique P0171 code keeps coming back

Tiny
BEN LEE
  • MEMBER
  • 1998 MERCURY MYSTIQUE
  • 4 CYL
  • 2WD
  • AUTOMATIC
  • 145,000 MILES
The code P0171 on my reader says "system too lean bank 1". After failing smog, I realized I would have to fix the check engine code instead of just clearing it for the test.

I failed the test due to NO being too high at 15 mph. Max for my car is about 450 and mine was at 611. I just barely passed at the 25 mph speed.

The following is what I have already replaced within the last week or so, which was all done to both bring down emmisions and hopefully remove the check engine light. Cleared codes after many of these repairs to see if the CIL would come back, so it has been on and off many times.

-added hose clamp to both ends of the breather hose(one end had only a zip tie, the other end at the engine had no clamp at all)
-replaced BOTH 02 sensors (upper and lower, realize now that was a waste)
-replaced the mass airflow sensor
-checked the egr valve (this was done by a mechanic, who said it was fine)
-new fuel filter
-checked fuel pressure and pressure regulator, which were within normal psi
-changed engine oil and filter
-replaced spark plugs
-replaced air filter and breather filter
-added a 16oz bottle of Lucas fuel system cleaner

I attempted to use the "soapy water" method to check for any hose leaks, but I did not find any issues, and was not really sure what I was doing or sure where to locate all the hoses that I might need to check.
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Tuesday, May 18th, 2010 AT 11:17 AM

22 Replies

Tiny
SATURNTECH9
  • MECHANIC
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First of all thank you so much for your donation. Sounds like you probably have a vaccuum leak thats about all you have left after replacing all the things you have.I would check for a vaccuum leak with some carb spray. What you do is let the car idle and spray the carb spray around all your vaccuum lines and intake manifold gasket also the base of your throttle body. If your idle goes up, down, stumbles, or dies you have a vaccuum leak there. Also what model Mystique do you have and what is your engine size?Let me know.
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Tuesday, May 18th, 2010 AT 3:30 PM
Tiny
BEN LEE
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Thanks so much for your prompt reply!
It is a 1998, 4 cyl, 2.0 engine (let me know if you need more info)

I had not heard of the carb spray method, so I'll definitely try that.

I did hear once that the "propane" method (similar to what you described) when used on a car with electronically controlled idle would not work properly since the electronic control would not let the engine's idle change, even though you are introducing fluid/gas into the engine.
Is that not correct?

I was just reminded that my engine, when idling, from time to time will almost stall very briefly (rpm goes down to 4 or 500 rpm), but then it goes right back up and no problem. It only does this once or maybe twice each time I'm out driving, and it is only while idling.

One thing I forgot to provide was the freeze frame data from my code reader after the light went back on in the most recent instance (not sure if that will help you or not.)
Fuelsyst1: CL
Fuelsyst2: n/a
load_pcs % : 56.9
ETC (*F): 189
Shrtft1(%): 14.8
Longft1(%): 7.8
RPM (/min): 1630
VSS(mph): 40

I should also mention that I cannot find the EGR on my engine, and my Hayes book specifically says that the 1998 models are not equipped with them, but my mechanic not only said that all cars after the 1970's have them, but also that he checked mine and that it was fine. But again, I cannot locate it under the hood at all

Again, thanks very much!
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Tuesday, May 18th, 2010 AT 3:43 PM
Tiny
SATURNTECH9
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https://www.2carpros.com/forum/automotive_pictures/416332_1998_mystique_code_p0171_1.jpg



https://www.2carpros.com/forum/automotive_pictures/416332_1998_mystique_egr_diagram_1.jpg


No its not true that on a computer controled idle you cant spray around looking for a vaccuum leak.So spray all around with the carb spray to see if you have a vaccuum leak.I also posted the trouble tree for your p0171 and posted a diagram for your egr valve.ley me know what you find.
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Tuesday, May 18th, 2010 AT 8:27 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
Thanks for the diagram.

I sprayed all around the engine, and especially tried to focus on hose connection areas, but I did not notice any changes in the idle.

If I can't find a leak, then that would leave:
-Restricted air cleaner (is this just referring to the air filter assembly?)
-Faulty PCV system (how do I check this system?)
-Incorrect cam timing (how do I check this? Or is that way beyond the scope of the DIY'er?)

I'm also wondering why the check engine light seems to be coming on more quickly after less driving than it used to. Before I started all these repairs, it would take between 30-40 miles of driving for the light to come back on after the battery had been disconected. And when I used my code reader to clear the code most recently, it took only 2 or 3 miles for the light to come back on. So either way, whether by disconnecting the battery or by clearing the code w/ the reader, it is coming on much more quickly than before all these repairs were done.
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Wednesday, May 19th, 2010 AT 10:26 AM
Tiny
SATURNTECH9
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For restricted air filter there talking mainly about a really dirty air filter. But if you had a kink or restriction in your air tube going to your throttle body or something like also.A faulty pcv you remove it and inspect it for a weak spring or all gummed up faulty hose etc. As far as checking timming you would have to remove the valve cover and line up all your timming marks lets wait on that one. We also have the excessive internal engine wear which you would do a compression check to check that. Also have you egr valve to check. Let me ask you this does the code always reset at cruise like 40 mph range you showed me on the snap shot?Let me know.
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Wednesday, May 19th, 2010 AT 1:25 PM
Tiny
BEN LEE
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I found the PCV valve coming off the oil separator on the front of the engine, but did not get any idle changes when spraying the connections as best as I could (was difficult since the bottle does not spray at all angles). But where does the other end of the PCV valve tube lead to, opposite the oil separator?

I still can't find an EGR, and the one shown in my Haynes book looks just like the one in the diagram that you provided to me, but I still can't locate it. My mechanic did say that he checked the EGR (this was a few days ago) and that it was fine.

And to answer your question: I think the previous time I wrote down all the freezeframe data the MPH was about 60 (I've only copied down my freezeframe data twice at this point)
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Wednesday, May 19th, 2010 AT 1:43 PM
Tiny
SATURNTECH9
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https://www.2carpros.com/forum/automotive_pictures/416332_1998_mercury_mystique_emmissions_1.jpg


I post the emmissions equipment your car should have you have to locate your vin letter or number for your car depending which letter you have you might not have a egr.When you find it refer to the chart i posted.As far as your pcv i couldnt find a picture or diagram for it.But the other end should go to a vaccuum source.Let me know what your find.
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Wednesday, May 19th, 2010 AT 5:48 PM
Tiny
SERVICE WRITER
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Let me throw a few things out on this.

The intakes on these can leak after getting hot and without a smoke machine it can be hard to track. So do your testing with the carb cleaner while hot. Keep in mind carb cleaner is flamable so use good judgement.

Several years back we had a contour (sister car to the mystique) that had a lean condition that was tough to find. It did take the smoke machine to find it. There is a plastic tube that runs down the back of the engine compartment between the motor and the firewall that was cracked. It rubs against a main engine harness and creates a vac leak in this plastic hose. We had to have the car in the air on the lift to find it. It is a dealer part. I'll see if I can get more info later on it.

This car should not have an egr valve.

One word of caution, Mass air flow sensors were a problem with many ford products. Because you replaced it, does not mean it is good. Primarily if this is a reman one.
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Thursday, May 20th, 2010 AT 5:19 AM
Tiny
SERVICE WRITER
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The part number of that tube I referred to is:
5rz2420ba
That is a ford # and must come from them.
It runs from the brake booster I believe.
Assuming it is leaking of course.
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Thursday, May 20th, 2010 AT 7:10 AM
Tiny
BEN LEE
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How would I confirm whether the MAF sensor is now working properly or not?

I have sprayed everywhere that I can reasonably get to with the carb spray, but no changes in idle. I'll have to see if I can inspect that tube somehow that you mentioned (behind the firewall).
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Thursday, May 20th, 2010 AT 9:47 AM
Tiny
SATURNTECH9
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https://www.2carpros.com/forum/automotive_pictures/416332_mass_airflow_sensor_1.jpg


Dont pay attenion to the part that says code will set under these conditions.It explains how your mass air flow sensor works.If your scanner will read live engine data you can use your mass air flow readings to find a leak.What you do is hook up your scanner to read engine data scroll to your mass air flow readings and while your spraying around at idle watch your fuel trim readings if they changed alot like what i just posted then when you stop spraying it goes back to where it was then you have a vaccuum leak.Also look into what service writer told you i asked him to give me a hand with your car.let us know what you find.
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Thursday, May 20th, 2010 AT 2:56 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
My code reader is the cheaper kind that only provides code#'s and freezeframe data, but I'm now planning to take it back and exchange it for one that provides live data feed.
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Thursday, May 20th, 2010 AT 5:02 PM
Tiny
BEN LEE
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  • 66 POSTS
Update: today was the last day for me to get a free re-test, so I reset the CEL to see if I could pass with lowered emmissions based on the work I have done thus far. The CEL stayed off, but my emmissions were about twice as bad compared to my first teset, which was BEFORE I did just about all these repairs and maintenance. Nitrous Oxide were both doubled at both 15 and 25 mph (last time I passed at 25mph, but failed at 15mph by about 160ppm)

Since it is MUCH worse than last time, I'm inclined to believe that the new MAF sensor is completely bad, and working even worse than the first one was. I will probably be changing it out again to see what happens.
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Thursday, May 20th, 2010 AT 7:18 PM
Tiny
SATURNTECH9
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Check out this scanner theres even a video to watch I think you will really like it. Its only like 20 more then the one you showed me it also shows your cars emission readness which would come in handy for you. You can even shop around and maybe find it cheaper. Sorry to hear about your smog check you could very well have a bad mass air flow with that new one. Looks like you can return that other one to habor frieght within 30 days for a full refund. The one you showed me looks like it will do live data and all that but the one I posted for you to look at looks alot nicer. Let me know what you think.
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Thursday, May 20th, 2010 AT 8:22 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
Thanks so much. That one does look better and I think I'll order it along with a Chilton book for my other car (Dodge Ram)

Speaking of. For a 2006 Dodge Ram 1500, do you think the Chilton book is better than the Haynes book? The chilton is about 200 more pages, but I have heard that it is less detailed without enough photos. I have a Haynes book for my '98 mercury and I like it, but when I noticed how much thicker the chilton book was, it got me to wondering.
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Friday, May 21st, 2010 AT 1:11 AM
Tiny
SATURNTECH9
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I think you will like the scanner I showed you. As far as the books go I haven't used a chilton or haynes for many years because I had acess to the factory manuals and alldata which is online information that shops get for there labor times, parts prices, and repair information. But when I did use them I always liked the chiltons. Sometimes its just a matter of ones prefrence I would look at both and see which has more usefull information for you.I would get the one that has the most detailed information like wire diagrams, emission diagrams etc.
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Friday, May 21st, 2010 AT 3:29 PM
Tiny
BEN LEE
  • MEMBER
  • 66 POSTS
Got the car passed for SMOG today, finally! It was the MAF sensor that was keeping the check engine light on. I've driven over 100 miles since it was changed (for the 3rd time in 2 weeks) and no CEL and the smog numbers were back to normal. Aparently the first 2 sensors that were used for replacement were worse than the original one.

I do have one other issue at the moment that I'd like to diagnose, which is the RPM's dropping at idle once or twice each time I'm out city driving for 15-20 mintues. It goes down to about 4 or 500 rpm and shakes the engine, but it never dies and comes right back up after one second.

Thanks for all your help everyone!
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Tuesday, June 1st, 2010 AT 5:31 PM
Tiny
SATURNTECH9
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What a mess you had all those bad maf's a nightmare to diagnose. So did you ever get that new scanner?If you did you can try it out for your idle drop set the scanner up to record live data and then when you come to a stop and it starts acting up hit the record trigger. Do you have any new codes check that also for me. Let me know.
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Tuesday, June 1st, 2010 AT 7:21 PM
Tiny
BEN LEE
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  • 66 POSTS
Still haven't gotten the scanner. May have to hold out until later in the year since some other expenses came up and I can't afford it right now, but I'm saving the link that you sent me and as soon as I'm ready that's the one I'm going to buy.

I'm trying to build up a list of diagnostic equipment so I can have a decent selection of tools for doing my own diagnostics. What is currently on my list or that I have already is:
-fuel pressure gauge
-vacuum pump/pressure gauge
-oil pressure gauge
-compression tester
-mulitimeter
-Innova scanner

What else would you recommend for general diagnostics?
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Wednesday, June 2nd, 2010 AT 9:43 AM
Tiny
SATURNTECH9
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I would add to the list a power probe 3 test light I have one and love it. It has a digital screen to tell you exactly what voltage you have on the wire or circuit your testing. It tests high enough to even test the hybrid battery packs. You can also add power or ground to a circuit to see if that's the problem has a built in circuit breaker. Tells you if you have power or ground to the wire or circuit it's really nice. As far as the oil pressure gauge not really a popular tool at least with the saturns I have worked on thru the years. The compression tester is nice to have but I wouldn't get one unless you needed one. Also did you know autozone rents compression testers and other tools like that for free you pay a deposit of the tools retail value and when you return the tool they give you a full refund. They even have the vacuum pump you have on your list fuel pressure gauge as well. So I wouldn't worry about getting those.I would get the scanner because they only rent a plain code reader.I would get the multimeter and the test light save you some money since you don't do it for a living you just need the bare essentials. You could also get a spark tester there pretty cheap and nice to have. But they rent a nice selection of tools at autozone you should check it out even I was impressed by what they rent.
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Wednesday, June 2nd, 2010 AT 2:27 PM

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