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Thread: e28 535is m30 rough idle, compression not great. Help please...

  1. #1
    Join Date
    Aug 2013
    Location
    Seattle, WA
    Posts
    59
    My Cars
    '02|e28|e34|e85|e39|e90

    Thumbs down e28 535is m30 rough idle, compression not great. Help please...

    Hi all,

    I just picked up a 1988 535is 5 speed! I have wanted one of these for years, but couldn't find an affordable one until now. However this one was/is in need of help. When I bought it two weeks ago it was not running, was moldy, mossy, dirty, etc. Sitting for a long time. I now have it clean, scrubbed, clay-bar'd, waxed and running, and on its way to being a real car again. I've attached some pictures the paint is crap from the front fenders backwards, but I still love the way this car looks. I am, however, having idle problems that I am not sure if I can solve so I am turning to you guys for expertise and help.

    The car starts up cold and runs fairly okay (with a more solid idle), but as it starts warming up, it starts misfiring and idling rough - shaking the car. When driving, the misfiring reduces and is not as noticeable unless the the car is rolling in gear with low power applied to the throttle. Then it'll randomly misfire. I have also noticed that when accelerating, in the low RPM range there isn't much power and it seems to come in waves a small bit. Not much, but if one pays attention, you can feel it. If the throttle is held at a higher rpm, say 2000 rpm, the misfiring is still evident and there will still be random kicks.

    The other day I changed the spark plugs and tested compression before I put them in. The numbers are less than pleasing... I then figured that maybe after the years the rockers may have come out of adjustment so I pulled the valve cover and adjusted the clearance for each. None of them were too loose, some were too tight, and some were just right. I did the compression test with a fully charged battery, a battery charger providing 15A constantly and the throttle open. Here are the numbers:

    Pre valve adjustment
    1 - 110 psi
    2 - 110psi
    3 - 90psi
    4 - 95psi :/
    5 - 90psi
    6 - 120psi

    Post valve adjustment
    1 - 120psi
    2 - 110psi
    3 - 87psi
    4 - 95psi
    5 - 90psi
    6 - 125psi

    As you can see the results are fairly disappointing. And I was disappointed to find that the valve adjustment didn't really do anything. I don't have a leakdown tester and I've never done a leakdown test before, but I am not sure what help that would be at this point.. I spoke to the previous owner (2nd level back) and he said in 2013 the car ran like clockwork and all compression was within 5psi. 6 years later the car is lower on compression.

    Anyway here are the things I've done:

    1) Swap the ECU - this is what got it running. The previous ECU would dump massive amounts of fuel into the motor without any spark
    2) Oil change with valvoline 20w50 vr1 racing oil.
    3) Change the spark plugs with NGK copper gapped to 0.032in
    4) Change fuel filter
    5) Inspect the spark plug wires, but there was no evidence of corrosion
    6) I ran a bottle of seafoam through the intake and it didn't really do anything.
    7) I replaced the boot between AFM and throttle and also the boot pre AFM to airbox.
    8) I sprayed starter fluid around the motor to see if it had a vacuum leak and I couldn't find one.
    9) I did valve adjustment, tightened up the oil sprayer banjo bolts, and got a new valve cover gasket.
    10) I tightened the oil pan bolts, which were coming loose.

    The car does have:
    1) An aftermarket ignition coil
    2) Bremi spark plug wires
    3) The ignition coil to distributor wire isn't the proper one, but it does make plenty of contact.

    So do you guys think that the rough idling is due to bad compression, or would the m30 still idle with these numbers. I am hoping it is the latter.

    Any help is appreciated!


    IMG_20190505_194040.jpgIMG_20190505_203543.jpgIMG_20190504_213628.jpgIMG_20190504_170338.jpgIMG_20190504_233824.jpg

  2. #2
    Join Date
    Jun 2018
    Location
    MT View, HI
    Posts
    167
    My Cars
    '80 733i , '76 2002
    Way to clean that beauty up! Nice.
    I can't help with your idle, as I'm fighting a lumpy idle myself. Mines the opposite, rough when cold. Those test numbers don't seem horrible, these are low compression smog motors. I am thinking mines a vaccum leak that I am missing. Just ordered a eBay smoke machine. Around $60 delivered. Can't hurt to have.

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