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Thread: 733i High Idle

  1. #1
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    733i High Idle

    Trying to get me '84 to pass smog. Idle is currently too high to test.

    On cold starts, the car starts and idles around 600 and slowly raises as it warms up, stopping around 1300.

    Is it normal to idle that low on cold start? Everything else is smooth. No major fluctuations. I sprayed everything with carb cleaner and saw no noticeable changes. Where should I start?


    Thanks!
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  2. #2
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    Idle control valve is likely the culprit, or coolant temp sensor and or vacuum leaks. Most likely one or a combination of those. Search is your friend on this, lots of good information​, don't get into adjusting anything related to air/fuel, idle screws or anything, your idle is controlled by the ECU, something is throwing it off.
    Last edited by kojo96; 04-04-2017 at 12:43 AM.

  3. #3
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    This is the coolant temp sensor on the thermostat housing. Either the sensor is bad or the connection is not good. I would clean the connection first and if that doesn't fix the problem check the sensor for proper resistance at the temp of the housing. It is the blue sensor.

  4. #4
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    Quote Originally Posted by 8991XJ View Post
    This is the coolant temp sensor on the thermostat housing. Either the sensor is bad or the connection is not good. I would clean the connection first and if that doesn't fix the problem check the sensor for proper resistance at the temp of the housing. It is the blue sensor.
    Am I measuring across terminals? As the car sits cold in my driveway, I'm showing 0 ohm

    CORRECTION: Shows open across terminals
    Last edited by dunnright7; 04-04-2017 at 06:14 PM.
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  5. #5
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    The Bentley says the temp should be 2100-2900Ω for 68°, 270-400@176 and 7000-11600 @ 14°F for the 533i temp sensor.

    Open is bad, makes car think it is the wrong temp. Yes measure across the two terminals.

  6. #6
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    I lied. It actually reads 2500 cold (about 70 degrees) and 230 hot. This multimeter seems to be a bit inaccurate in general, but are these readings decent enough?

  7. #7
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    those reading are fine so clean the connection to that and then you need to verify that if BMW did a service update on that coolant temp circuit it is still intact. A service was performed that put a resistor in line with the coolant temp sensor to raise the resistance to smooth the idle. Usually the boot for the sensor was peeled back and the resistor was soldered in to the wiring harness. I have seen one that the resistor came loose, equals no CTS signal, yields cold start at regular idle, increasing idle as it warms and 1300 rpm idle warm, no hot restart. Pic in this thread: http://www.mye28.com/viewtopic.php?f...55704#p1355704

  8. #8
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    Resistor is still intact. Other than the high idle, everything else is fine. No issues with hot starting or anything.

    It seems like the CTS is functioning somewhat fine. When I unplug it while the car is hot, the idle lowers, but it fluctuates a bit and stalls if you give it any gas.

    Should I be looking into the TPS as a potential culprit?
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  9. #9
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    Alright. I'm resurrecting this thread because 5 months later, I still haven't gotten this thing fixed. Work and school have kept me away from it for a while, so I pulled the car out of storage and got it running again this morning. As expected, same as before. Starts cold at about 700 RPM and slowly climbs as it warms. I have the warm idle down to just over 1k now. I've replaced almost all of the vacuum lines and other rubber bits including injector seals. I also replaced the CTS earlier this year.

    Is there a procedure for testing the idle computer? I feel like that's the last thing I've left untouched at this point. I really need to get this fixed so I can smog it and start driving it. It's killing me to have it sitting for so long.
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  10. #10
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    On a motronic car idle is controlled by the Idle control valve, if it's not working nothing you do will give you a correct idle- Pull it out of the housing it's in, disconnect the plug, holding it in your hand and rocking it side to side you should feel the valve opening and closing, there is a voltage test also, google that I don't remember what the readings should be.

    TPS (on throttle body is only for idle and off idle, should click JUST when throttle is opened- there is also a voltage reading on that- Start with the ICV-

  11. #11
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    Quote Originally Posted by kojo96 View Post
    On a motronic car idle is controlled by the Idle control valve, if it's not working nothing you do will give you a correct idle- Pull it out of the housing it's in, disconnect the plug, holding it in your hand and rocking it side to side you should feel the valve opening and closing, there is a voltage test also, google that I don't remember what the readings should be.

    TPS (on throttle body is only for idle and off idle, should click JUST when throttle is opened- there is also a voltage reading on that- Start with the ICV-
    The ICV seems to function. When it's off the car, it rattles when I shake it. If it is disconnected while the car is running, the idle starts fluctuating and it runs like crap.

    I double checked the TPS adjustment and it checks out as well.
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  12. #12
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    Vacume leaks...

  13. #13
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    Quote Originally Posted by kojo96 View Post
    Vacume leaks...
    I've replaced every piece of rubber in sight. Sprayed the crap out of it with carb cleaner too. I'll smoke it tomorrow and report back.
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  14. #14
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    Smoke test yielded no visible leaks. Can some sort of fault in the idle computer cause the issue?
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  15. #15
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    I think that car has a separate controller for the idle speed valve. Little green box about 2/3 the size of a pack of cigs above the glove box. I may have a spare in some old parts.

  16. #16
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    I think ^'s talking about the ignition control module, not even sure that car has one, even if it did I doubt it's the source, those either work or not, and if not car won't start.
    Has the car been basedlined? If not then this might become an ordeal for you, hard to diagnose not knowing what's been done/changed, there are so many factors that could affect the cars ability to run correctly.
    I'd start with what is known good, without question, that'll help you and others chime in on how to help.
    I just went through this on my car, running good, then bad, then better... I basically went through everything, if it was suspect I replaced it, now the car is running really well, and if it hiccups again I'll be better able to diagnose it.
    Unfortunately, on these older chassis, there's a $2k rule, (think that's outdated now as parts are getting more expensive) what it costs to get a car running as it's supposed to, and that's doing the labor yourself,... This takes away any questions about what could be wrong, nothing worse that throwing new parts at a car hoping for it to run right.
    List what you know is good, your car should be running Motronic 1, do you know condition of plugs, wires, cap, rotor, both speed and cps sensors on bell housing, vacuum lines routing correct?, All sensors on t-stat in working order, o2 sensor working?...
    On a side note, if on a cold start your getting 600-700 rpm, CSV might be suspect as would be that sensor.
    Also, is your HVAC working correctly? Check the vacuum lines that feed the HVAC under the hood, manifold line that runs across the engine bay, also the black air storage tank under the vent cowl, known leaks there.
    Last edited by kojo96; 09-18-2017 at 10:37 PM.

  17. #17
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    One way to rule out the vacuum leak is to get a cheap handheld vacuum pump (probably $20), put a "t" connector in any vacuum line, connect the pump and pump it up. If it doesn't hold vacuum, then you have a leak somewhere. If you have a leak it will cause the symptoms you described. Like kojo69 said, it could be a line or connector under the cowling.

  18. #18
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    No, I am NOT talking about an ignition module. It is a small green box about half the size of a pack of smokes.
    It is the module that controls the idle only on 83 and 84 3.3 engines in E23, E24, and E28.
    Your idle control valve is only half the equation. If the controller does not work, it doesn't matter if the valve is good or bad, you will have either erratic idle, or very fast idle. NORMALLY, but not always, when the green box goes bad, the idle goes sky high. I had one that was just erratic on an 84 733i, and, after replacing the green control module, idle smoothed out perfectly, and stayed working fine until 380,000 miles.

    - - - Updated - - -

    This part: https://www.bavauto.com/catalog/prod...yABEgLUK_D_BwE

    PART#: 13 41 1 286 133.

    I guarantee you it isn't an ignition module. Its only function is to control the ICV.

    BTW, not suggesting you go out and purchase one for $400 plus. Someone on here probably has a known good one they can loan you.
    Last edited by lynnbilodeau; 09-20-2017 at 09:52 PM.

  19. #19
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    Quote Originally Posted by lynnbilodeau View Post
    No, I am NOT talking about an ignition module. It is a small green box about half the size of a pack of smokes.
    It is the module that controls the idle only on 83 and 84 3.3 engines in E23, E24, and E28.
    Your idle control valve is only half the equation. If the controller does not work, it doesn't matter if the valve is good or bad, you will have either erratic idle, or very fast idle. NORMALLY, but not always, when the green box goes bad, the idle goes sky high. I had one that was just erratic on an 84 733i, and, after replacing the green control module, idle smoothed out perfectly, and stayed working fine until 380,000 miles.

    - - - Updated - - -

    This part: https://www.bavauto.com/catalog/prod...yABEgLUK_D_BwE

    PART#: 13 41 1 286 133.

    I guarantee you it isn't an ignition module. Its only function is to control the ICV.

    BTW, not suggesting you go out and purchase one for $400 plus. Someone on here probably has a known good one they can loan you.
    That's the part in question. The price is basically what is keeping my from throwing a new one at it. So if anyone does have a known good one they'd either part with or even loan out just for diagnostic purposes, I would be very interested.
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  20. #20
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    What's the complete part number on yours? Can you post a pic?

  21. #21
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    Quote Originally Posted by lynnbilodeau View Post
    What's the complete part number on yours? Can you post a pic?
    P/N per RealOEM is 13411286134

    Pic attached

    20170925_090518.jpg
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  22. #22
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    That is the idle control module, same as the 533 & <9/87 528 had, they are problematic and all fail eventually.
    --Jay3->Sic gorgiamus allos subjectatos nunc
    84 €735i manual, 88 528e/i
    Motronic 1 and 1.3 wiring
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  23. #23
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    I probably have two or three, but they are at my brother's shop, and I don't get by there very often these days.
    There is a VERY SLIGHT possibility that I have on here at the house in a box marked "Misc. BMW parts". I will look and see, but normally only keep parts here that might fit one of our drivers, and we have no 83 or 84 cars right now other than my turbo, which does not use that part.
    If I have one, you can have it for free. However, whatever I have has been sitting for at least 10 to 12 years, so no guarantee.

    I may make it by this weekend, and if I do, will look in my giant stash up stairs.

    Keep your fingers crossed.

  24. #24
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    Quote Originally Posted by lynnbilodeau View Post
    I probably have two or three, but they are at my brother's shop, and I don't get by there very often these days.
    There is a VERY SLIGHT possibility that I have on here at the house in a box marked "Misc. BMW parts". I will look and see, but normally only keep parts here that might fit one of our drivers, and we have no 83 or 84 cars right now other than my turbo, which does not use that part.
    If I have one, you can have it for free. However, whatever I have has been sitting for at least 10 to 12 years, so no guarantee.

    I may make it by this weekend, and if I do, will look in my giant stash up stairs.

    Keep your fingers crossed.
    I ended up grabbing a $40 working unit on eBay yesterday. Pretty cheap, and you can't beat 1-day free shipping. I guess I'll know this afternoon if that was the issue.

    Thanks for the offer though!
    1978 320i | sierrabeige
    1975 2002 | granatrot

    1966 Volvo 122S
    2015 Volvo V60 R-Design

  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 if I can figure out how to. 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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