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  1. #1
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    Member No: 116551 villam10 is an unknown quantity at this point villam10's Avatar
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    Engine shakes/hesitates while idling and the car is in motion...pls help.

    2003 BMW X5 4.4
    Engine shakes/hesitates while idling and the car is in motion...for example while you're slowing down for a red light and then it turns green...the car is rolling at low speed I press the accelerator that's when it shakes/hesitates for a second or two before it takes off normally. I took the car to the dealer and had them scan it...it gave the code for the O2 sensor (upstream before cat converter bank one). We replaced the sensor with a Bosch O2 sensor. The car ran fine for a day or two and then started shaking again...I figured I would replace the other side as well just to make sure but no luck fixing the problem...the dealer scanned it again and no codes came back...I can't afford to have the dealer check it all the time (I pay $190 every time they check it). Long story short the same problem persists and I'm not sure what to do about it...my only guess is I might need to change the fuel filter....maybe?
    Any help is appreciated...
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  2. #2
    Robert Platt Bell
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    Check for intake leak

    There are a number of "O2 Sensor" codes, and knowing which one is the key to diagnosing the problem.

    And that is the word - DIAGNOSING.

    Warranty Monkeys at the dealer insert the code reader, and if the code MENTIONS a part by name, they replace it.

    This is idiotic.

    But not as idiotic as taking any car to a DEALER once it is out of WARRANTY.

    Find a good independent BMW mechanic who charges less and knows what he is doing. Warranty Monkeys at the dealer know little about how to fix older cars. They deal with recalls and TSBs and most are fresh out of BMW mechanics school. Seriously - look to see how young they are.

    Again, there are a number of "O2 Sensor" codes. One is when the heater wire BREAKS, and yea, that usually means replace the O2 sensor, although sometimes it can be a loose connection (a bad connection reads the same as an open circuit on the heater wire).

    A very typical code is "Oxygen sensor adaptation limit reached, bank X" which does NOT mean the O2 sensor is bad.

    Again, OBD II codes tell you the SYMPTOM, not the PROBLEM - and any mechanic who merely reads codes and the replaces parts is not really a mechanic - but a monkey.

    What causes this code and what does it mean? It is caused by a too-lean mixture. The computer tries to "adapt" the system to the mixture, but reaches the limit of adaptation and then bombs out, goes into "safe" mode (running rich) and sets off the CE light (in most cases).

    A leak in the intake elbow (a rubber piece that attaches between the MAF plumbing and the intake manifold) can cause unmetered air to enter the system. This will trigger an CE light and the "O2 sensor adaptation limit" code to be set.

    And this code will appear only intermittently. I had it pop up about every six months, then every three, then two, then one. I finally fixed it.

    AGAIN: (and please beat this into the head of your "mechanic" at the dealer): Just because an OBD II code mentions a part by name does NOT MEAN the cure is to "replace part".

    BTW, this intake elbow is a $15 to $30 part. Yea. And another user here e-mailed me that his dealer wanted to replace ALL FOUR O2 sensors for $1500 and he checked and sure enough, it was the intake elbow.

    Diagnostic tools are just that - tools. They are not a substitute for using your brain to determine what is causing the codes.

    For example, "Catalytic Converter Efficiency Below Threshold, Bank X" might sound like an expensive Catalytic converter problem, right?

    Wrong. In this case, the culprit is usually the Oxygen sensor!

    BTDT, in both cases..... And I've seen people spend $$$ replacing perfectly good catalytic converters this way, too - going to crappy aftermarket jobs that don't work right, when all they needed was an O2 sensor.

    Find a good independent mechanic who knows how to work on older BMWs.

    Dealers are for Warranty work, PERIOD.

    Good Luck!

    P.S - Fuel Filter, Perhaps. It is a PITA to replace. I counted about 28 bolts to remove the splash shield below the gas tank. The filter itself takes 2 seconds, but you get a 92 octane shower. Don't smoke. I replaced mine at 100,000 miles and it probably was unnecessary. Unless you are using Mexican gasoline (which has sand it in), the fuel filter is probably OK, unless you have high miles on the car.
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  3. #3
    Registered Member
    Ft. Worth, TX, United States
    Member No: 13623 tcachtung is an unknown quantity at this point tcachtung's Avatar
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    www.bimrs.org get that vehicle properly diagnosed. The dealer has very few good techs with diagnosing abilities espcecially when your plans are only diagnostic...they don't give a damn if the diagnosis is correct or accurate since they are not repairing it.
    Trent Cole @
    Lone Star Bavarian
    3800 West Vickery Blvd
    Fort Worth, Texas 76107

    Bosch Authorized Service Center
    Member of BIMRS.org, 12 years
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