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Re: <E28> lurking secondary problem.. hunting idle

Christopher Graff Wrote:

Well, I don't know what you did for the previous issue, so I'm going to
start from the beginning...


1. Check all vacuum leaks.

Thorough Check done when ICV issue was going in (car stalling out at idle)
no leaks.  All vacuum tubes removed, checked, bellows checked, and
reinstalled.

2. Start up seems normal, cold idle should be at about 1000 rpm, but
then should drop to the 'normal' 800 rpm.

The car previously (to idle stall problem) started normally, and then returned
to idle (700 RPM?) but intermittently did this same thing after a long drive
1-2 hours or more.. Idle at 1000-1100, hunting etc.  and as soon as the car
cooled off the problem would be gone.  Now the problem seems to be constant

3. The Motronic is sensing something is wrong, when you say that the
rpms drop to 600ish, then rise to 1000. Also, it is trying to compensate
for something by doing the 600 to 1000 rpm hunting.

4. Check ICV operation. Replace if bad.

ICV was previous problem, and was removed, cleaned with carb cleaner and
reinstalled.  Solved stall at idle problem.  I know I have to replace it.  but
I suspect its a fairly expensive part so.. I am hoping to get away with it for
a while before buying another.

5. Check the throttle flap stop, make sure it is set to spec (see
Bentley).

Will check, but still dont have a bentleys, as car was just back on road as of
friday, and there was a national holiday here on monday (canada)

6. Check the operation of the throttle position switch (either by elec.
tests in Bentley, or see if it 'clicks' when you move the throttle off
of idle - do it with the engine off, otherwise you won't hear it).

It clicks!!

7. Adjust the TPS, for correct operation, check TPS (elec tests in
bentley), replace if bad.  Again No bentleys yet.  If someone could scan and
e-mail the specific pages I would appreciate it.

I feel it is something up to this point (specifically something to do
with the TPS). The reason I say this is that you describe the symptom of
'pulling' the car along at idle - there is not enough power at idle to
really 'pull' the car along, though you can have an open throttle at
1000 rpm, for instance, and the car will 'pull' along - thus I think
that from that symptom you describe, the Motronic is somehow recognizing
that you have the throttle open to 1000 rpm, even though your foot is
off the gas. You may think the throttle is closed, cuz your foot is off
the gas, but the car thinks that you have an open throttle to 1000 rpm;
and if it is a TPS problem, that will generally be the rpm it will occur
at, and if the TPS is maladjusted or bad, then it could go down to the
true idle - 600 rpm in your case as you describe - and oscillate between
that true idle and the 'opened' throttle position of 1000 rpm.

If you have not fixed the problem by going thru all these tests, and
adjustments, then it is not unheardof to be:

8. Check the AFM for smooth flap operation.

Will Check that in the Morning.

9. Swap out AFMs with a good known one (only true way to test if an AFM
is bad)

Unfortunately dont have another AFM for that test

10. Malfunctioning cold start valve

11. Bad coolant temp sensor

12. Bad thermo time switch

How do I test for 10, 11, 12?


Cheers
 Ron Jordan
 http://www.geocities.com/tatsu911/tshoot.html
 my online 535i troubleshooting page
 85 535i
 73 911s 2.7----- Original Message -----
  From: Christopher Graff
  To: [email protected]
  Sent: Wednesday, July 03, 2002 4:44 AM
  Subject: Re: [SIG@M535i] <E28> lurking secondary problem.. hunting idle


  > [email protected] wrote:
  > Well now that I am back on the road, after dealing with the ICV issue.
  > I noticed this weekend on the way to my camping destination that the
  > car (85 535i) started that high idle issue again.

  Well, I don't know what you did for the previous issue, so I'm going to
  start from the beginning...


  1. Check all vacuum leaks.

  Thorough Check done when ICV issue was going in (car stalling out at idle)
  no leaks.  All vacuum tubes removed, checked, bellows checked, and
reinstalled.

  2. Start up seems normal, cold idle should be at about 1000 rpm, but
  then should drop to the 'normal' 800 rpm.

  The car previously (to idle stall problem) started normally, and then
returned to idle (700 RPM?) but intermittently did this same thing after a
long drive 1-2 hours or more.. Idle at 1000-1100, hunting etc.  and as soon as
the car cooled off the problem would be gone.

  3. The Motronic is sensing something is wrong, when you say that the
  rpms drop to 600ish, then rise to 1000. Also, it is trying to compensate
  for something by doing the 600 to 1000 rpm hunting.

  4. Check ICV operation. Replace if bad.
  ICV was previous problem, and was removed, cleaned with carb cleaner and
reinstalled.  Solved stall at idle problem.

  5. Check the throttle flap stop, make sure it is set to spec (see
  Bentley).

  Will check, but still dont have a bentleys, as car was just back on road as
of friday, and there was a national holiday here on monday (canada)

  6. Check the operation of the throttle position switch (either by elec.
  tests in Bentley, or see if it 'clicks' when you move the throttle off
  of idle - do it with the engine off, otherwise you won't hear it).

  It clicks!!

  7. Adjust the TPS, for correct operation, check TPS (elec tests in
  bentley), replace if bad.  Again No bentleys yet.  If someone could scan and
e-mail the specific pages I would appreciate it.

  I feel it is something up to this point (specifically something to do
  with the TPS). The reason I say this is that you describe the symptom of
  'pulling' the car along at idle - there is not enough power at idle to
  really 'pull' the car along, though you can have an open throttle at
  1000 rpm, for instance, and the car will 'pull' along - thus I think
  that from that symptom you describe, the Motronic is somehow recognizing
  that you have the throttle open to 1000 rpm, even though your foot is
  off the gas. You may think the throttle is closed, cuz your foot is off
  the gas, but the car thinks that you have an open throttle to 1000 rpm;
  and if it is a TPS problem, that will generally be the rpm it will occur
  at, and if the TPS is maladjusted or bad, then it could go down to the
  true idle - 600 rpm in your case as you describe - and oscillate between
  that true idle and the 'opened' throttle position of 1000 rpm.

  If you have not fixed the problem by going thru all these tests, and
  adjustments, then it is not unheardof to be:

  8. Check the AFM for smooth flap operation.

  Will Check that in the Morning.

  9. Swap out AFMs with a good known one (only true way to test if an AFM
  is bad)

  Unfortunately dont have another AFM for that test

  10. Malfunctioning cold start valve

  11. Bad coolant temp sensor

  12. Bad thermo time switch

  How do I test for 10, 11, 12?


  Cheers
   Ron Jordan
   http://www.geocities.com/tatsu911/tshoot.html
   my online 535i troubleshooting page
   85 535i
   73 911s 2.7

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