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1995 M42 idle issues

Discussion in 'E36 (1992-1999)' started by steven s, Nov 1, 2013.

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    steven s

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    High idle

    I've replaced a couple cracked hoses and will probably disassemble the intake manifold to clean the throttle body, ICV and replace whatever other hoses are down there.

    In the mean time I bought some carb cleaner to see if I can find some leaks.
    Intermittently the idle will jump around while driving.

    Today I noticed idle is around 800 when I first start the car.
    As it warms up the idle is closer to 1300,

    Does that tell anyone anything?
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    charlson89

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    I would start by checking for intake leaks.
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    steven s

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    Finally got around to working on my idle problem.
    Remove the upper intake manifold.
    Low and behold. Three of the four hoses vacuum hoses to the fuel injectors are cracked.
    Another hose going to the bottom of the manifold is not even connected.
    Another hose is crumbling.

    I clean the ICV. Replace the hoses.
    I still have a high idle.

    When I start the car it's around 800-900 rpm. After I drive a bit, it idles closer to 1300.
    Needless to say my gas mileage sucks!
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    MGarrison

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    Mileage? I think I've heard that icv's may get to the point where cleaning is only temporarily effective, which leads me to think maybe they get to a point of not working effectively even when freshly cleaned? Maybe that's true-er for E30 icv's...

    Bentley manual have any suggestions you haven't tried yet?
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    steven s

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    164,000
    I was so sure the cracked hoses was the problem.
    I didn't mind replacing them since they were needed. PITA though. :)

    Could also be a Throttle Position Sensor?
    It looks like it's the same one use on my M52 so I could possibly swap them out.

    Could also be a bad MAF?

    Could be a bad ICV.

    Could be a vacuum leak that I can't find.
    The hoses are tucked below the upper intake manifold.

    02 Sensor?

    The fact that it idles fine on start up and then fast after it's warm should mean something.
    Didn't see anything in the Bentley manual.
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    MGarrison

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    Smoke test for vacuum leaks... isn't that where you blow smoke around the engine and see if anyplace that might have a vacuum leak tends to suck the smoke in? The problem for me would be coming up with smoke, since I literally can't hack cigarettes or, worse, cigars.

    If you have any wiring diagrams for the ignition & fuel systems, I'd say try and decipher what the icv-related inputs & outputs are to see if that helps any with diagnosis.

    One time my E30 wouldn't idle steady, just big up & down revs, made it really difficult to drive on the street. Replaced dang near everything, finally swapped in an ecu, which fixed the problem - something to do with the idle control in the ecu was bad. I don't think that sounds like your issue. I'd guess some input is out of range or off and causing the issue. Wish I knew more about it to be more help!
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    steven s

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    Thanks.
    I may just through a new ICV in there. From BMW it's more than $300.
    I found another place at 1/2 the price.
    I'm sure the K&N had something to do with it.
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    Ken.S.330

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    steven s

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    Replaced the regulator valve on the intake manifold.
    Still a high idle.
    I don't think it's a vacuum leak anymore.
    Next up on the list to order, a new ICV.
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    steven s

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    So I get a new ICV.
    When I took apart the manifold I noticed the hose disconnected from the ICV to intake.
    Maybe I forgot to connect it when I pulled the ICV to clean?

    Anyway. Since I have a new ICV I replace it.
    Very rough idle. Smell gas in the exhaust. Throw a CEL.
    Decide to go to sleep.

    Next day I remove and reassemble.
    The vacuum T-tree isn't positioned properly because I cut my own hoses to the fuel injectors.
    The angle is off by a few degrees.
    The hose from the tree to the ICV keep coming off so I wire tie it.

    Reassemble.
    Idle at 800 on start up as always.
    Engine idling smooth now.
    I don't think I had the upper intake manifold secured to the bottom.
    Note to self: Don't work in the dark. :)

    Drive for about 10 minutes. Idle still at 800.
    Hard to tell if it was a bad ICV all along.
    Just about every vacuum hose was previously replaced.
    ICV seem to be pretty typical failures anyway.

    Now to see if my mpg goes up.
    In the winter I got 20. Now that it's a little warmer I'm getting 22.
    I'd like to see high 20s city.
    charlson89 and MGarrison like this.
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    Raphaellacerda 98 318i “why don’t I have a steering tilt?”

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    Could a leak on the air pump hose or the pump itself cause a high idle ?
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    steven s

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    Secondary Air Pump?
    None of my cars have a SAP but I don't think that would cause a high idle.
    I believe the sole purpose is emissions on start up.
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    steven s

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    My gas mileage continues to decrease. I smell gas in the exhaust.
    Now my idle goes down at lights and very sluggish and a random CEL.
    Initially it's OK. Seems once the motor is running for 10 minutes the problem occurs.

    When I initially scanned the code I got Emission (lambda) control.
    Ignored it for some time until it's gotten progressively worse where I can't even drive it.

    Today I decided to go over previous work.
    I replaced the homemade vacuum tree from the ICV to fuel injectors with a OE that are molded properly.
    Same problem.

    Replaced an 02 sensor. Same problem.
    I'm waiting on a fuel filter to replace also.

    For kicks I scanned the codes again.
    This time
    Knock sensor, Cyl 3-4
    Oxy sensor

    Well I changed the 02 sensor before clearing the codes.
    Looking at replacing the knock sensor. Looks like a PITA job on some motors.

    The car sounds like a diesel.
    Could it be a clogged cat that caused the knock fault?

    Add:
    I've been told to remove the 02 sensor temporarily to determine if something is clogged which might account for the knock sensor fault.
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    MGarrison

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    No miss or running rough? Seems like something like that would indicated something spark/ignition related, which could mean raw gas. Otherwise, something that's making the DME dump more gas than is necessary, or, perhaps downstream - I don't know if clogged cats would end up causing unburned gas or not.
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    steven s

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    Engine will shake a little. It all starts after 10 minutes or so.
    I do have what I feel as a miss when accelerating.

    I may have to trust the fault codes for now even though something else can be triggering the fault.
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    steven s

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    I pulled the O2 sensor out leaving it connected.
    Ran the car for maybe 10 minutes.
    Idle dropped once but there seems to be a lot of pressure coming out of the sensor hole. Hard to tell what's normal. Hardly anything coming out of the tailpipe.

    Rescan the codes and now I have Knock control regulation.

    Reinstalled O2 sensor. Cleared codes.
    Ran for about 10 minutes and idle started to drop again consistently with the same Knock control regulation fault.

    Stuffed cat and maybe not a knock sensor?
    Muffler?
    Resonator?

    Boy the exhaust gets hot quick.
    Got a nice little burn on my wrist.

    I have a good exhaust shop I can bring it to.
    I suppose I can have him remove the cat to inspect and install a straight pipe if it's bad until I replace the cat.
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    charlson89

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    Sounds like you have a misfire causing the noise and the exhaust to get super hot really quick. The reason your getting a knock faults is from the misfire the DME is actually catching the knocks and telling you about it. It could be like garrison said spark issue or fuel. From the running for 10 minutes first it sounds like a issue when your in closed loop and not in open loop. I would unplug the mass airflow sensor when it starts running bad and see if it improves or gets worse.
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    steven s

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    Baffled.
    Rough idle and stalls after 10 minutes with O2 sensor.
    Remove O2 sensor to allow pressure to escape in case clogged cat.

    Now runs for only 3 minutes until rough idle and almost stalls.
    Disconnect MAF, idle smooths out. That's almost $500!

    From the exhaust fumes, running rich.

    Installed the O2 sensor.
    Ran the motor for 10 minutes with the MAF disconnected.
    Idle stumbled a little but not as bad as before.

    Cleared fault codes.

    Reconnected MAF. Ran for 10 minutes, no problem.
    Fuel burning better I guess since the O2 sensor was reconnected.

    Rescan codes
    Knock control regulation
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    MGarrison

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    I wonder if cleaning the MAF might help?

    http://www.autozone.com/autozone/ac...or-cleaner/_/N-262e?itemIdentifier=36011_0_0_

    Interestingly, the cautionary statement with their product listing says "This item cannot be shipped to any US State, US Territory or US Military address." Kinda makes ya wonder how THEY get it into the stores! (yes, I know, licensed certified shipping exception or some-such, but, still) :D
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    steven s

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    I'll take a look but still get the Knock control regulation fault.

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