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Charles Bogie asks
>This car was built late 1987,  is a 1988 model with the motronic 1.1.
>Car has 140,000 miles and the problem started about a year ago....
>I hesitate to call this problem an idle problem as it is not what is
>describled in the FAQ, however, the symptoms occur right around idle
>speed.  As the throttle is opened (and the idle position switch opens)
>the RPM goes from an idle immediately to about 1500+.  There seems to be
>no middle ground. Throttle response is smooth on up.
>Then, as the throttle is closed, RPMs drop smoothly until about 1500 and
>then a sudden drop to idle (about 750) as the microswitch closes.
>As you can imagine, this makes for very annoying driving on the highway.


Subject: RE: Sensitive throttle with A/C on

Hi Guys,

You want a solution to your problem???? The following may help.


  • First off make sure your O2 sensor is working properly
  • 2nd remove the idle valve and hold with the electrical piece facing up, get a can of Brake Kleen and spray and shake (rotational shake so the idle actuators internals move) until it is free and all the carbon is out.
  • Make sure your Throttle position switch (TPS) is working, can you hear it click when the throttle is opened off the idle position, if no it needs adjustment or replacement, if yes attach a DVOM to the center connector and to the idle contact (trial and error if you do not have a schematic) use the continuity test, this will tell you if the switch is working electronically ( the best test for it is a voltage drop test spec: not more than 0.7V). The symptom if this is not working is a fluctuating Idle as the idle signal come from the AFM only and the intake pulses act on the AFM flap.
  • Check the AFM flap for crud etc. and clean out the flap chamber with the Brake Kleen and check for free movement.
  • So once you have checked and verified that these and the AFM are OK check the CO/HC is within specs
  • get whoever is going to do this to perfom this next piece too or if you are so inclined DIY, it is not written down anywhere but it works.
      while you have everything apart clean out the throttle housing,
    • adjust the throttle flap so there is a 0.05mm gap between the housing and the flap on the trailing side,
    • adjust the idle position switch to engage (contacts close) 1mm before it hits the stop when closing. (Oh you will have to re & re the housing to do this properly)
    • refit all and do not connect the Throttle position switch connector,
    • Jump the connector from the center contact to the idle circuit contact ( you will have to have a schematic to see which is the right one for your car)
    • start the car, actually you will know if you are in the correct contact if you try and rev the engine and it is in the correct way it will not rev above 1100 or 1200 RPM, the other one is the full load contact and it will allow you to rev up.
    • You also need to have a DVOM connected to the idle valve connector (back of the plug while still connected to the idle valve ) and you will need the yellow/white wire (there are some that the green/red is the one but don't worry about that just yet)
    • put the red probe from the DVOM into the back of the plug (Yel/Whi) and the black probe to a good ground and make sure it is secured. (Make sure the red probe or the yel/whi wire does not touch ground otherwise say bye bye to your CU)
    • When you have all this set up make sure the O2 sensor is hooked up and start the car,
    • let it idle until it reaches operating temperature and switch the DVOM to Frequency (Hz) what you will need it Duty Cycle and it should show you 36% or close to if it is +_ 1% it will be ok if it is any more you can fine tune it from the flap adjustment screw on the top of the flap linkage (no more than an 1/8th of a turn either way form when you set the 0.05mm gap as you will have to set the Throttle postion switch again) If it is at 36% great you should already notice a better idle you will also get better cold start characteristics. (also check this with the A/C on it may vary a bit but not to much, when you put the A/C on , let the idle stabilize for a minute or two). Remove DVOM and the jump wire from the TPS and reconnect.
  • This should help in your idle problems. this adjustment will go out as the crud builds up again so I suggest you have it done every Inspection 2. Your dealer (if you are in the U.S. probobaly will say do not touch it, as that is what they have been told via BMW NA) but I know for sure it works, as dealerships in Canada do it and it works, they did it on my car, and explained to me what they were doing. It takes about an hour to do it all properly.
  • Another thing would be to disconnect the DME or the battery to get rid of the adaptives stored and see how the car runs then (most prob worse) the adaptives can take up to 45mins of driving (domestics call this "block learn") before they are fully adapted to the new settings.

Hope this helps


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