CEL P0171, Loping/Surging Idle, Engine Vibrations - What do they mean?

[clumsy]

Hello,

Car: 1999 Contour, 4-Cylinder, 162k miles. I have received so many conflicting opinions about my problem from laymen and mechanics. I need help.

About three weeks ago CEL P0171 (System too lean, bank one) came on. The car wasn't running perfectly, but until that light came on I assumed age was the cause.

Someone suggested cleaning the MAF sensor with spray so I did. A few days went by and nothing changed, and I was told to try the PCV valves, the upper O2 sensor, the lower O2 sensor, the fuel system, and that "it's probably a huge problem and we'll need all day to look at it." That was a shop owner.

I was eventually persuaded to replace the lower O2 sensor first. I bought one from Autozone, but I couldn't get the lower one off as it seemed to be screwed in, somehow. At that point I found CEG, where I learned through searches I should replace the upper. I went to return the lower and Autozone insisted they sold me the upper. So I went back to replace the upper but the plugs didn't fit. The O2 sensor from Autozone had a round plug and the O2 sensor on my Contour had a D-shaped plug. I went back to Autozone again, but their computer did say they had sold me the upper sensor for a 1999 4-Cylinder Contour. He didn't know what else it would be. But it doesn't fit!

About a week and a half ago, the engine started loping after a few minutes of driving, but only when the car is stopped. Above 5-10 MPH there is no problem, or at least it is no longer noticeable. It happens 60-80 times per minute. It happens quicker when the car has been driven recently (heat?) Sometimes it is strong enough that the "troughs" cause the car to die. I have no problem instantly restarting it.

1. Should I replace the O2 sensor, and if so, how do I get the right part from Autozone?

2. What else should I try replacing?

3. What do I risk damaging by not addressing this problem really quickly? I don't have much money and don't know a trusty mechanic, but if I am out of time I guess I will bite the bullet.

4. Is this really obvious?

Here is a link to some pictures. I hope they will speak clearly where I was unclear. They are about 500k each in size.

http://www.flickr.com/photos/25741071@N04/sets/72157604782109298/detail/

 

[mrutkaus]

Not familiar with 4 cyl but the loping on a 6 cyl would probably be the idle air control IAC.

Mike

 

[stuukaatz]

P0171 - trouble shooting

P0171 - trouble shooting

I just ran into this problem three weeks ago and finally resolved it this past weekend ( in that 120 miles plus and no CEL. Engine read out, NO CODES!! lol). I hope what follows helps you out. My vehicle is a 1996 Mystique, but with 4 cyl., 2.0 engine and I believe what I say here holds true for your vehicle as well. Ok, here goes. First things first. P0171 is thrown for one of two reasons, 1) insufficient fuel - be it a injector issue or pressure issue, etc, or 2) a vacuum leak - usually on the intake side of the engine after the MAF sensor. I did a ton of research on this problem and finally resolved it.
Judging from the low speed "loping" the engine is making, I'm inclined to believe you have a vacuum leak. I tried the "easy" remedies first; cleaning the MAF sesnor didn't work. I even went to the junk yard and got a replacement MAF off a Contour with only 42,000 miles on it, didn't make a difference. My second step was the O2 sensor before the Catalytic Converter. Replaced it with a new one, didn't make a difference. For your situation, screw what the Autozone guy says, take the O2 sensor off your car and bring it to him and show him exactly what you need. Although replacing the O2 sensor didn't resolve my problem and probably won't resolve yours, you spent good money...get the right one, replace it and be done with it.
Now comes the fun part. These next two items, PCV valve and replacing vacuum lines are relatively inexpensive but are time consuming and "labor intensive". First, I started with the PCV valve as it was listed as one of the next most logical steps and it needed to be changed anyways (was over it's suggested life span). The PCV valve is located behind the Catalytic Converter, attached to the engine and is inbetween the Oil Separator and a metal tube that leads to vacuum line. Autozone has a pretty good explanation of how to remove and change PCV valve in it's repair guide section. It's a pain in the ass to get to, but I'm glad I changed mine as it was really full of sludge. I cleaned the Oil Separator with carb cleaner, changed out the PCV Valve ($3.00) and cleaned out the tube to the PCV valve. I cleaned out the tube first by disconnecting the vacuum line at the opposite end and spraying carb cleaner through it. I also ran a thin piece of string through it, starting at the end where I removed the vacuum line. Once I saw the string come through the end where the PCV valve goes, I started tying knots (about 4 of them every two inches or so) and then grabbed each end of the string and ran the knots through the tube back and forth with more carb cleaner. Cleared out a lot of gook (sludge) in that tube.
The next item I tackled was checking/replacing vacuum lines, both rubber and plastic. An old time trick I used helped identify one of the leaks, but not the other. With the car securely parked and your engine running, spray carb cleaner around the vacuum lines, intake manifold mount, throttle body mount, EGR vacuum lines, EVR vacuum lines, etc,. If there is a vacuum leak, the carb cleaner will enter the line and cause the engine idle to surge/rev. I found a cracked line behind the throttle body this way. I also found a "hairline crack" in the upper plastic vacuum line mounted along the firewall/cowl. A quick trip back to the junk yard where I had found the 42,000 mile Contour and I confiscated as many of the hoses as I could as they were all in rather pristine condition. I changed out the two known bad hoses as well as any others that just looked old and weathered. Car is running like a champ now, no CEL, no codes of any kind. Things are looking good...lol. So, long story short, maybe try the carb cleaner trick first as it may be a really obvious bad hose (vacuum leak). Note, you can replace the plastic vacuum lines with rubber ones if you want. Oh and remember to disconnect the negative side of your battery terminal when working on your car. For safety reasons as well as resetting the PCM. Well, good luck and hope this helps.

 

[clumsy]

Update:

Replacing the upper o2 sensor didn't fix the problem. Carb cleaner seemed to say the fuel injectors were leaky. I read Chilton on fuel injectors and decided to take it to a recommended mechanic instead of risking it myself.

It turns out there were two problems with similar symptoms. First, a vacuum hose was ripped. Second, I had a bad MAF sensor (wasn't obvious until the hose was fixed). I replaced the sensor and everything is working great! The car is quiet and smooth, and the CEL is gone. Everyone, thank you for your help.

(By the way, this mechanic is easy on the budget. He called me up and told me to buy and install the new MAF sensor myself. His bill was $90, and the MAF was $90 at Autozone with 1yr warranty, so I am satisfied.)

 

[iskoos]

Good to hear that. Wish I could be that lucky. I did many many thing and still couldn't find the problem I am having at idle (erratic, stumbling idles)

Would you happen to be in Orlando so I can go see this mechanic?

 

[clumsy]

Sorry, I'm in Illinois. I hope you can solve your problem without spending too much. From reading this site, I'm amazed how many different emissions/intake problems have similar symptoms.

 

[iskoos]

Illinois!.. Guess I will pass this by...

I did many things but at the end didn't spend much money bacuse I returned most of the parts back to store if it didn't the problem.
What I spent is my time and being without my daily driver...

It hurts...