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rough idle and stalling

Discussion in 'E24 (1977-1989)' started by eric266, Apr 12, 2009.

    eric266 guest

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    I'm still trying to get my 84 633 running properly, I have resolved several issues but still have one that I simply can not figure out. Maybe you guys could help. The car starts fine and runs okay until it gets warm, then the RPM's start to hunt between 800 and 1000 RPM then the engine starts to stumble and dies. If I punch the gas it hesitates but will normally get up to speed. If I ease into the gas it hesitates and stumbles worse.

    Things I've changed or checked out:
    Cap, rotor, plugs, and wires
    Thermo-time switch
    Temp switch
    Idle control system
    ECU
    main and internal fuel pumps and filter
    flywheel sensors
    Oxygen sensor
    Vacuum lines, boots, hoses, etc
    And just about everything else in the Bentley manual

    Any help would be greatly appreciated!!
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    mooseheadm5

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    Clean the ICV and make sure there are no vacuum leaks. The idle control system can cause running issues. Also check the TPS for proper adjustment.

    eric266 guest

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    I have a new ICV and replaced all the vacuum hoses and looked for additional leaks, I did find the oil pressure sender on the back of the head leaking oil out of the spade connector changed it and the problem got a little better but is still there. I will check the TPS. When I adjusted the valves I noticed there was a LOT of sludge build up. I have flushed out the motor twice with fresh oil. Would sludge build up on the valves cause my problem??

    Thanks,

    Eric
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    mooseheadm5

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    Maybe carbon buildup in the combustion chamber, but the ICV system is a known issue on BMWs of this vintage. You can try to bypass it temporarily to test it. Remove the ICV. Get a plumbing end cap that you can fit into the hose and drill an 1/8" hole into the plug. Install it into one of the lines and connect the lines together with a pipe fitting. This will give you a smallish idle oriface and allow you to see if the idle remains stable (though maybe a bit low or high.) If your problems go away, you are looking at replacing the "green box" that controls the ICV.
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    mooseheadm5

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    Also, you may wish to check to see how smoothly your AFM door moves. That can cause problems like this as well.

    eric266 guest

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    I've changed the green box as well. I did check the TPS as you suggested and it worked fine in the idle and mid range but when I got toward the full throttle it did not work as advertised, not sure if that would effect idle but I'm going to go ahead and change it. I've done every check in the book twice and everything else works. The only thing I have not done yet is pull out the fuel injectors and check spray pattern. Guess I will do that this weekend right after I double check compression to make sure I don't have an issue. Thanks for the help!! From here on out the she will be known as "lucy" short for Lucifer!!!

    Eric
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    KALMUSI

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    Sorry I didn't get on this forum sooner and share.

    How have you made out since your last post?

    I have an '83 633 an have had idle problems since I bought it in Sept of 1990. I have changed the ICM (Green Box above the glove box) 3 times and each time it has worked for a few years and then gone bad again.

    After the usual tune-up items didn't help the idle, I cleaned the ICV with "Radio Shack Tuner Cleaner." This improved things, until the original module failed.

    My first two replacements were Programma rebuilds in 1991 and about 1995. Both failed.

    The last swap I did was a ICM and ICV set from the 325e/538e. The valve fits correctly, but is the not the "proper" all black color - which bothered my "all original" sense, but I got over it. It was cheap - about $80, but only lasted a couple of years. The car will start, warm up and idle fine for about 30 minutes of driving, and then will stall at idle. I believe that heat builds up in the ICM, and it loses it's ability to open the ICV.

    For "limp home," I unplug the ICV, which leaves it open. With the throttle closed, the engine revs between 1000 and 1500 RPM. I understand this is the Engine Management Computer cutting off the fuel and restarting it. If you unplug the ICV, and you get the same results - stalling, etc. then you may have other problems. If you replaced the ICM with a used unit, you probably did not resolve the issues.

    It sounds like you have been though everything - Spark plugs, spark plug wires, distributor cap & rotor, ignition coil, vacuum hoses, valve clearances, etc. I'm guessing the engine runs like a top with your foot on the gas? Mine does - nobody passes me, unless I let them. You may need a new ICM.

    Unfortunately, new ICM (which needs a new ICV as well for compatibility) are $600. The thing is, I don't want to waste my money on an improperly designed part that will fail again in a few years.

    The real problem is the ICM is an analog circuit that depends on the values of resistors and capacitors to measure the engine speed and control the ICV. With age and heat, these components change value, and this screws up the "formula." The ICM also uses a power transistor barely capable of handling the current needed to pulse the ICV. This part can also fail or work intermittently and is sensitive to heat.

    Starting in '85 the 5/6/7 Series no longer have an ICM - the ICV is controlled by the Engine Management Computer - which is a digital "computer" circuit that needs only accurate sensors to calculate the correct ICV pulse width to maintain the idle speed.

    I am building a replacement ICM using a tiny single board computer that will fit in the green box. Since it is a digital system, it is not dependent on any heat sensitive components. The ICV will be controlled by a new type of transistor - called a MOSFET - that does not heat up in use, and can handle 40X the current drawn by the ICV.

    My original ICV works fine on my test bench connected to my new digital idle control. I hope to install the new ICM in the car this weekend, and the put the nice all black "correct" ICV back in as well. My ICM will actually work with either the original ICV or a replacement from the 325e. I will gladly give up the "original" ICM for one that works, and lasts.

    eric266 guest

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    I finally got the car to idle fairly smooth a few weeks ago. When I adjusted the valves after I got the car i noticed there was lots of sludge in the top end of the head, I double flushed the engine and thought I had gotten rid of most of the sludge but it did not make any difference in the idle. As a last chance before I was going to give up and tow it to the shop I added CD2 engine detergent to the oil ran it for 10 minutes let it sit over night. Next morning the car started and idled high (900) but smooth as silk. Only thing I can think if is I had a sticking valve causing a vacuum leak? readjusted the valves and reset the ICV to get the idle down to 800RPM. I do still have a hesitation problem at around 2500-3000RPM but I think the fuel system is causing that. The tank has some rust in it and I think it is restricting the fuel filter, going to pull the tank out this week and have it cleaned and sealed. All of this trouble because the PO let the car sit for almost a year! I just replaced the ICV and ICM trying to fix this problem. Let me know how your digital ICM works out, sounds interesting!!

    Eric
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    mooseheadm5

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    Let me know how well that idle control works. There is a market for it.
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    KALMUSI

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    Kalmus Digital Idle Control

    It has taken way too long, due to my modern life, but my '83 633CSI is now up and running on my Digital Idle Control Module. A tiny computer, running a program I wrote, is monitoring the engine RPM and opening and closing the ICV to maintain proper idle.

    Since I did not have a working OEM (VDO) module, I had to experiment to find the operating parameters. I have my laptop connected to the Kalmus Digital Idle Control (KDIC) so I can see what is going on, and make the needed tweaks. I pull over and stop, of course. I'm working on a design that will fit in the original "green" box. It will not be able to be connected to an external PC, but once I get all parameters set right, I won't need a laptop as a co-driver.

    During testing, the intake developed a major air leak, which I traced to two conditions. The "fuel" line connecting the expansion tank to the charcoal canister split and opened, and the Air Flow Meter's output flange got crushed by years of over-tightening the hose clamp (guilty!) It looked like an egg with several humps. Hours of squeezing in a vise and careful pounding got it back to an almost round shape. The engine runs smoother, quieter, and with better low-end torque.

    I plan to write an article and hopefully get published in Roundel, and tell the whole story. I'll post again the story develops.

    Ira

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