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Thread: 1984 633 CSI erratical idle

  1. #1
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    1984 633 CSI erratical idle (with video)

    Hello everyone , i picked up my shark 2 months ago with an idling issue from previous owner that i'm trying to short out. The car starts right up and idles normal until the temp rises to about 150-160F . The idling then becomes erratical and rpms jump from 1000-2000. When driving i'm experience no lack of power , hesitation or anything unusual . Its when the rpm drop to 1000 that she idles bad. First i looked the Idle Control valve. I had it cleaned and adjusted the screw but nothing changed. I replaced the hose connecting it with manifold because it was cracked . None of the above changed anything. When i disconnect the ICV nothing changes .
    I have attached a short clip of what it does . Does anyone had similar symptoms on their shark?
    Thanks in advance for your help

    Last edited by Mitsos; 01-24-2016 at 09:13 PM.
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  2. #2
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    From the image in the video, you are missing the ICV. This valve controls idle speed, and cannot do without. See this pic...circled item....

  3. #3
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    ...and if you took the ICV off and there is no change, then the ICV is frozen. You can try cleaning it..if you shake it with a twisting motion, you should hear/feel the circular valve inside moving freely.

  4. #4
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    Hmmm for some reason , my ICV looks different and is located underneath the big intake hose .. when i took it out and cleaned it , i could hear the valve moving freely inside while i was shaking it
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  5. #5
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    My pic is from an 85 E24 M30 B34 (on a stand in my garage). Real OEM also shows this type. IMO, either the IAC is not working, or you have more vacuum leaks somewhere. Could be the big flap in the Air Flow Meter is not closing, or the spring in the AFM is loose. There is also a hex screw on the bottom of the AFM, but this is for idle mixture, and would not cause such a high idle.

    When it's idling, pull the 90 degree rubber boot off between the air cleaner and AFM and see if the flap is oscillating with the idle speed.

  6. #6
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    Quote Originally Posted by Dschart View Post
    My pic is from an 85 E24 M30 B34 (on a stand in my garage). Real OEM also shows this type. IMO, either the IAC is not working, or you have more vacuum leaks somewhere. Could be the big flap in the Air Flow Meter is not closing, or the spring in the AFM is loose. There is also a hex screw on the bottom of the AFM, but this is for idle mixture, and would not cause such a high idle.

    When it's idling, pull the 90 degree rubber boot off between the air cleaner and AFM and see if the flap is oscillating with the idle speed.
    Thank you for your input Dschart , i will check it out this week and post back !
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  7. #7
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    Be sure to have a look at the throttle body to make sure its not dirty with buildup keeping the butterfly from closing completely. Also there are vacuum fittings on the bottom of the manifold to check. Even the oil filler cap and dipstick has seals. These engines are very sensitive to vacuum leaks. Possibly the throttle cable or cruise control cables are holding the tb butterfly open.

  8. #8
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    Quote Originally Posted by Dschart View Post
    Be sure to have a look at the throttle body to make sure its not dirty with buildup keeping the butterfly from closing completely. Also there are vacuum fittings on the bottom of the manifold to check. Even the oil filler cap and dipstick has seals. These engines are very sensitive to vacuum leaks. Possibly the throttle cable or cruise control cables are holding the tb butterfly open.
    Thanks for pointing out to check the throttle body . Would that cause the rpms to jump up and down only after warm up?
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  9. #9
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    I think it could. The ecm is using an open loop base map when cold. When the water temp rises, the ecm goes into closed loop and tries to achieve 14.7 air fuel ratio. It could either be very rich or lean when cold thus limiting rpms. When in closed loop, the ecm could be dealing with vacuum leaks and has a hard time controlling the mixture thus causing the swings.

    From your video, I hear a lot of abnormal engine noise. I would check the valve clearance and timing chain. Take the valve cover off. Check that valve clearance is in spec. Check the 2 oil bar banjo bolts are tight. Look at the cam lobes for wear. Check that the cam sprocket bolts are parallel with the head deck when the damper is on OT. Check the timing chain for slop.

    I've had 3 M30 engines. All 3 needed banjo bolts replaced with the updated loctite design. All 3 also needed the timing chains replaced.

  10. #10
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    Quote Originally Posted by Dschart View Post
    From the image in the video, you are missing the ICV. This valve controls idle speed, and cannot do without. See this pic...circled item....
    The OP has an 84 model which has different injection than the 85 and newer as posted in your picture. The early motronic uses an air valve under the intake boot and idle control unit mounted separate under the dash. The control unit has been known to give issues.

  11. #11
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    I would add. The ECM needs to have a good O2 sensor, speed pickup sensors, temp sensor, throttle switch, all inputs that have an effect on idle cotrol.

  12. #12
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    I have an 84. Mine will do this with the dip stick pulled out so verify the dip stick seal is intact and tight to the tube. Also check the oil filler cap seal. I believe you can swap the gas cap for the oil cap to see if it helps. Verify 12 volts is getting to the plug on the ICV. If the valve cover itself is leaking, it would do this as well. The engine is noisier than mine so check the valve adjustment as mentioned as well as the oil tube bolts. You have a vacuum leak somewhere.

  13. #13
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    The hunting idle could very well be a lean condition (vacuum leak). Your cold start valve keeps the engine rich on startup, but when the valve shuts off you could be in a lean condition due to unmetered air, although I haven't seen one hunt that significantly

    Maury.

  14. #14
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    Quote Originally Posted by alpinacsi View Post
    The OP has an 84 model which has different injection than the 85 and newer as posted in your picture. The early motronic uses an air valve under the intake boot and idle control unit mounted separate under the dash. The control unit has been known to give issues.
    Thanks for pointing it out !Its one of the parts i need to check
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  15. #15
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    Quote Originally Posted by mauryc View Post
    The hunting idle could very well be a lean condition (vacuum leak). Your cold start valve keeps the engine rich on startup, but when the valve shuts off you could be in a lean condition due to unmetered air, although I haven't seen one hunt that significantly

    Maury.
    Yes, vacuum leak. I'd put a vacuum gauge on it and see what it reads.

  16. #16
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    Also, the pictures and diagrams of ICV's above are for a 635, not a 633. They are totally different between the B32 and B34. The B32 has a smaller, silver ICV beneath the central intake boot. The B34 has the ICV pictured that connects to the central intake boot. Just to clear that up.
    1986 635CSi - 2001 330ci

  17. #17
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    Sounds like a vacuum leak. The sporadic idle sounds like you're pulling out the dipstick while engine on.
    Tom
    Present: '06 530xiT | '00 RD R50 |'88 635CSI (project) | '85 635CSi

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    ...

  18. #18
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    I realize there are quite a few possibilities when diagnosing your problem but you may want to check your engine ground straps. My 87 325 had similar idle issues after warmup and I discovered a loose strap from a previous repair. I tightened the bolts at each strap end and my idle problem was instantly fixed. Grounding straps also wear out with age.

  19. #19
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    Quote Originally Posted by f16driver View Post
    I realize there are quite a few possibilities when diagnosing your problem but you may want to check your engine ground straps. My 87 325 had similar idle issues after warmup and I discovered a loose strap from a previous repair. I tightened the bolts at each strap end and my idle problem was instantly fixed. Grounding straps also wear out with age.
    Thats something i would have never thought. I'm currently restoring my cluster(gears bulbs and SI batteries) and havent got a chance to troubleshoot my idle issue . Looking forward to check all this out soon .
    Your input is much appreciated !
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  20. #20
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    Finally the winter weather is taking a break and i was able to go out try to diagnose what is causing the hunting idling on my shark. So the other day I unplugged the coolant temp sensor and she stopped hunting but kept idling higher than normal. I plug it back in and she hunts again . None of that at cold start while the cold start valve keeps the mixture rich . I ordered and replaced that coolant temp sensor but the problem persists .
    Im a bit lost at this point ..
    The Oxygen sensor light is on and i will replace the O2 sensor tomorrow see if that changes anything

    https://www.youtube.com/watch?v=RHAvSjB5Rq0
    Last edited by Mitsos; 03-06-2016 at 11:32 PM.
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  21. #21
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    a week later i have replaced the coolant temp sensor , coolant temp switch and the O2 sensor. Still getting this haunting idling once warms up. I swap the ICV from another 633 and still same. I then tested the connector of the ICV and i get no power . I think this the problem. Anyone can point out where this connector is getting power from??
    Thanks in advance
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  22. #22
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    Exclamation My shark start Hunching after warm up.

    Quote Originally Posted by Mitsos View Post
    a week later i have replaced the coolant temp sensor , coolant temp switch and the O2 sensor. Still getting this haunting idling once warms up. I swap the ICV from another 633 and still same. I then tested the connector of the ICV and i get no power . I think this the problem. Anyone can point out where this connector is getting power from??
    Thanks in advance
    Hi This is Henry
    I now have same problem with you. I have changed O2 sensor, Temperature sensor, throttle body, air valve,Injector,Air flow sensor,DME,checked wire coming connected, coming out from DME for leak=No leak, New High tension lead for spark plug,distributor cap, distributor roter.
    Still hunch after warm up.
    Did you fixed your shark? If you did please let me know how you did it.

  23. #23
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    Check the ICM... Not the ICV- your idle is controlled by two items, the idle control valve (ICV under the intake tube) and an idle control module (ICM). A hunting idle on an early m30b32 533i/733i/633i is almost always one of those two parts, this assuming no vacuum leaks.
    Not sure where on an e24 it's located but in my 533i it's above the ECU in the glove box, original is a Black module, replacement is Green.

  24. #24
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    Module is in Same location as above on a 633. About 3"x3" module.
    Last edited by bmw6fan; 04-13-2019 at 11:37 AM.

  25. #25
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    Hey.. Did you ever this figured out.. My dad has a 1984 733i that does the same thing. It will start fine and then once warm it will have an erratic idle up and down from 1300 rpm to 700 rpm pretty constant. I have checked the IAC and its a bit of a different one that I have seen online.. It takes power to close it and is plastic with only 2 ports. When I apply 12volts to it , it does close and you can hear and feel it. We did replace some vacuum lines and tried replacing the IAC module and so far nothing has worked. I did notice that when I disconnect the coolant temp sensor it stops the idle from oscillating but the idle remains high.. Also notice if I remove the oil filler cap on the valve cover the idle smooths out more. I am curious if it just all the sudden with the coolant temp sensor unplugged it goes to a factory default open loop setting. I will try and attach a picture of the IAC.. Curious if anyone has one that is known to work. My dad has a shop manual but it talks mostly about the 1985 735i which is a different set up

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