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  1. #1
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    lack of power, rough idle on '95 540i

    According to my Snap-On scanner, it is setting four codes. The thing runs fine until it sets these codes, and then I can't even pull out into traffic it runs so rich.
    It will run fine for a few days, then runs like crap until I clear the codes. The first thing I did was replace the spark plugs. Removing the old plugs confirmed that it was running too rich. The codes it's setting are 203-O2 sensor control 2, 201-O2 sensor control 1, 13-O2 sensor 1, and 12-O2 sensor 2.
    I initially decided to just change out the O2 sensors, until I saw the codes for O2 sensor controllers. Is there a seperate controller for the O2 sensor heaters perhaps?
    I have suspected this to be a vacuum problem, because that mileage gauge underneath the speedo dips to where you can't even see the needle when it's running bad, and I thought that gauge was directly related to vacuum. I did the carb cleaner spray trick around the intake areas of the engine and did not get any change. I am also getting some white smoke out of the exhaust when it's running poor, but I am not using water, so I am not suspecting a head gasket.
    I know this message is long winded, sorry, but if anyone can steer me in the right direction with those O2 sensor controllers, it would be much appreciated.


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    Mass airflow sensor


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    Vacuum leaks - one of our favorite subjects!!!!!

    Shel, do a search here for vacuum leaks. Those leaks commonly set oxygen sensor codes. This engine is very picky about that. Little teeny dumb hoses crack from the high underhood temps and leak erratically. The most common leaks are under and at each end of the intake manifold, all involve orange silicone seals. Not hard to fix, just a removal of the intake manifold which is time consuming.

    Thanks
    Rich

    95 540iA BMW
    94 S420 MB
    91 944S2 Porsche

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    Re: lack of power, rough idle on '95 540i

    I will have to take off the top covers and check for vacuum leaks underneath. Was it the vacuum/economy gauge on the dash that points to this as being the problem? Thanks for the input.

    I will keep you informed as to my discovery, probably tomorrow. I cleared the codes with the Snap-On Solus today, so hopefully she takes me home safely, lol!

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    White smoke = rear manifold plate/oil seperator.

    And also causes a big vacuum leak. Do a search for rear manifold plate,pcv valve or oil seperator. That's what my money's on...

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    Re: lack of power, rough idle on '95 540i

    Thanks for the info everyone. This is not my only mode of transportation right now, so I am not going to tear into it immediately, but I will let everyone know here when I find the problem. Again, thanks!

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    Re: lack of power, rough idle on '95 540i

    I finally pulled this thing out of storage... have to get it back on the road before it snows.

    Yesterday, I pulled off all of the decorative covers from the intake manifold and coil covers. I sprayed carb cleaner everywhere, focussing on the back of the manifold where the seperator is suppose to be. I did not get any running change, suggesting that there are no intake leaks.

    The car is setting one code immediately (203 O2 sensor #2). She is running great right now. If I could only count on it running good like this I wouldn't care. I individually tested the outputs from both O2 sensors. The computer sends out a reference voltage of 450 mV to both, and they output 450 mV at perfect exhaust gas conditions. They output up to 850 mV when rich, and down to 200 mV when lean conditions are sensed. As tested, both of mine were reading 350-450 mV. They did not seem to react as fast as I would like, but it could've been my o-scope to blame there. I do not have the equipment to do a propane test on them.

    I did some research on the oil seperator, pcv, etc. that was suggested last time I brought this up, but that's why I checked for leaks back there, with no luck.

    I am going to remove both of my O2 sensors today and clean them out using a torch and brush. I did get some info claiming that slow outputs from the O2s could be clogged up sensors on those. I will post back. If anyone else has a suggestion, please let me know. I would appreciate it!

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    1 out of 1 members found this post helpful. Yes | No

    i believe i can help

    on the rear of the intake manifold there is a pcv plate and on the driver side there is a hole and grommet that should be plugged up completely
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