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E34 (1989 - 1995)

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  #1  
Old 03-27-2014, 07:51 AM
E34_Obsession E34_Obsession is offline
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E34 Idle Problem

1991 525i, M50B25 non Vanos

Starts and drives excellent, however when warm, idles rough and often jumps or surges between 1-2k RPM randomly.

While driving, the car has no loss of power, not burning oil or coolant, and shifts fine (automatic), but when at stop lights it has a rough idle and surges sometimes until you start moving again then the engine behaves normal. Replaced ICV, did a smoke test and has no leaks, ECM is new as well, and compression readings on all six cylinders are where they should be. If anyone had an idea please let me know.

-Niklas
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1991 BMW E34 525iA

1999 Toyota Tacoma Prerunner Xtracab 2.7L

2008 Toyota Tacoma Prerunner DCSB TRD Sport

1995 Toyota Tacoma 2WD DX V6 - SOLD

1992 Toyota Pickup - SOLD

2003 Subaru Forester 2.5X - TOTALLED

2004 Subaru Forester 2.5XT - SOLD

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  #2  
Old 03-27-2014, 08:00 AM
E34ZombieHunter's Avatar
E34ZombieHunter E34ZombieHunter is online now
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Have you done the stomp test? See my signature.
Post the results or if you are unsure how to decipher the blinking of the light, post a video of you doing the test and we can tell you the code(s) and their meaning.

Have you tried a drive-ability sensor disconnect test?
Disconnect sensors while it is running and note a change for the better or worse. Reconnect and move to the next.
Better=that sensor is bad
Worse= that sensor is good
No change(when rough)=bad sensor
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If you want to get junkyard parts remember one thing, if it was wrecked you know it was running/driving. You may not know how well, but it was.
Quote:
Originally Posted by BMR_LVR View Post
So a synopsis of a normally operating fan clutch:

Engine stone cold - fan clutch engaged
Engine at normal operating temp - fan clutch disengaged (easily stopped with the newspaper)
Engine above normal operating temp - fan clutch engaged
STOMP TEST

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  #3  
Old 03-27-2014, 08:08 AM
E34_Obsession E34_Obsession is offline
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It's a 1991 model and therefore the stomp test does not work.

It is not throwing any code(s), no warning lights are illuminated.

As far as drivability test, disconnected the MAF, TPS, Temp sensor(s), various other sensors on the intake, and the 02 sensor as well, and the car drove awful.

Reconnecting everything, car drives fine... it's when it's warm and I sit at a stop light that it idles rough and surges.

I can post a video of the rough idling if you want, but as far as codes or warning lights, there are non. Car is not in "limp home" mode either.
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1991 BMW E34 525iA

1999 Toyota Tacoma Prerunner Xtracab 2.7L

2008 Toyota Tacoma Prerunner DCSB TRD Sport

1995 Toyota Tacoma 2WD DX V6 - SOLD

1992 Toyota Pickup - SOLD

2003 Subaru Forester 2.5X - TOTALLED

2004 Subaru Forester 2.5XT - SOLD

2005 Subaru WRX Sedan - SOLD
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  #4  
Old 03-27-2014, 08:14 AM
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E34ZombieHunter E34ZombieHunter is online now
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Quote:
Originally Posted by E34_Obsession View Post
It's a 1991 model and therefore the stomp test does not work.

It is not throwing any code(s), no warning lights are illuminated.

As far as drivability test, disconnected the MAF, TPS, Temp sensor(s), various other sensors on the intake, and the 02 sensor as well, and the car drove awful.

Reconnecting everything, car drives fine... it's when it's warm and I sit at a stop light that it idles rough and surges.

I can post a video of the rough idling if you want, but as far as codes or warning lights, there are non. Car is not in "limp home" mode either.
The stomp test does not work on 88-89 models, BUT that is only because they do not have the bulb but the wiring is there. Thus when a bulb is put in you can do the test.
Im not as familiar with the M50 idle issues, hopefully someone with the same past experience will jump in and help, and at the same time i will try to read up and provide more help.
Refer here to do the stomp test if you so wish to. After the code list.
http://www.bmwe34.net/E34main/Trouble/Engine_codes.htm
__________________

Gotta love an E34!!:thumb up:
If you want to get junkyard parts remember one thing, if it was wrecked you know it was running/driving. You may not know how well, but it was.
Quote:
Originally Posted by BMR_LVR View Post
So a synopsis of a normally operating fan clutch:

Engine stone cold - fan clutch engaged
Engine at normal operating temp - fan clutch disengaged (easily stopped with the newspaper)
Engine above normal operating temp - fan clutch engaged
STOMP TEST

OEM Approved brands
READ ME IM THE BIBLE
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  #5  
Old 03-27-2014, 08:42 AM
capricornbmw capricornbmw is offline
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I think you're supposed to disconnect one sensor at a time, reconnecting it before going to the next sensor, such that only one sensor is disconnected at all times.

If you unplug more than one at one go, your engine may turn rough anyway. I think this differs from engine to engine.

And zombie, that's a good chart, but can you reconfirm that disconnecting a sensor which results in an engine becoming worse, means that you've unplugged a bad sensor? Doesn't it mean you've unplugged a good sensor and so the engine is thrown off without it?

Interestingly I just had to do this yesterday. I felt and odd behaviour in the engine, unplugged the afm, for a short while the car seemed more responsive, but when I stopped and started flicking the throttle, the engine seemed to cough more. Then when I took off again it was no longer as responsive as the first time after it was unplugged. Stopped and plugged the afm back in again, cleared codes, and started up engine was much better. So I believe my afm should be ok.

What do you think? And another question...should the disconnect test be done live while the engine is running or should we only unplug (and reconnect the sensor previously disconnected) a sensor after shutting down the engine, and then starting up again to see its behaviour?
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  #6  
Old 03-27-2014, 08:43 AM
capricornbmw capricornbmw is offline
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Quote:
Originally Posted by E34_Obsession View Post
1991 525i, M50B25 non Vanos

Starts and drives excellent, however when warm, idles rough and often jumps or surges between 1-2k RPM randomly.

While driving, the car has no loss of power, not burning oil or coolant, and shifts fine (automatic), but when at stop lights it has a rough idle and surges sometimes until you start moving again then the engine behaves normal. Replaced ICV, did a smoke test and has no leaks, ECM is new as well, and compression readings on all six cylinders are where they should be. If anyone had an idea please let me know.

-Niklas
This is usually the icv, tps or vacuum leaks. Since your icv is new and there are no vacuum leaks, it is the tps confirmed. Unplug it and test its behaviour during idle. If the behaviour is just as bad, do me a favour plug it in again and unplug the icv and try once more.

And golly compression figures please tell us exactly what they were on your engine both wet and dry if you did both ! This is very relevant to another thread that's running here now.
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  #7  
Old 03-27-2014, 08:44 AM
E34ZombieHunter's Avatar
E34ZombieHunter E34ZombieHunter is online now
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Quote:
Originally Posted by capricornbmw View Post
I think you're supposed to disconnect one sensor at a time, reconnecting it before going to the next sensor, such that only one sensor is disconnected at all times.

CORRECT^^^ I believe that is what is says WORSE running=good sensor

And zombie, that's a good chart, but can you reconfirm that disconnecting a sensor which results in an engine becoming worse, means that you've unplugged a bad sensor? Doesn't it mean you've unplugged a good sensor and so the engine is thrown off without it?
CORRECT^^^^


What do you think? And another question...should the disconnect test be done live while the engine is running or should we only unplug (and reconnect the sensor previously disconnected) a sensor after shutting down the engine, and then starting up again to see its behaviour?
I have seen both methods, and i have done the AFM and TPS live and others while off.
.
__________________

Gotta love an E34!!:thumb up:
If you want to get junkyard parts remember one thing, if it was wrecked you know it was running/driving. You may not know how well, but it was.
Quote:
Originally Posted by BMR_LVR View Post
So a synopsis of a normally operating fan clutch:

Engine stone cold - fan clutch engaged
Engine at normal operating temp - fan clutch disengaged (easily stopped with the newspaper)
Engine above normal operating temp - fan clutch engaged
STOMP TEST

OEM Approved brands
READ ME IM THE BIBLE

Last edited by E34ZombieHunter; 03-27-2014 at 08:45 AM.
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  #8  
Old 03-27-2014, 08:46 AM
capricornbmw capricornbmw is offline
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Oops read too quickly. Just noticed that your issues only begin when the engine is hot. Then this could be the ects (blue tipped engine coolant temp sensor). I had weird idle some months ago until I discovered the ects had been left unplug (my bad, I forgot).

Try that OP. And please, only one sensor at a time.
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  #9  
Old 03-27-2014, 08:48 AM
capricornbmw capricornbmw is offline
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Oh I'm super crosseyed today. Sorry zombie. I mean when you unplug a sensor and there is no change. When I unplug my tps, I get a slight blip on my idle and then it stabilises almost immediately. No difference in driving (and no limp mode on my car). The tps is 1 year old oem.


Quote:
Originally Posted by E34ZombieHunter View Post
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  #10  
Old 03-27-2014, 08:57 AM
E34_Obsession E34_Obsession is offline
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I will try disconnecting the TPS and I'll look in to the Blue sensor within the next hour. Will report back. Thank you all for the feedback.

-Nick
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1991 BMW E34 525iA

1999 Toyota Tacoma Prerunner Xtracab 2.7L

2008 Toyota Tacoma Prerunner DCSB TRD Sport

1995 Toyota Tacoma 2WD DX V6 - SOLD

1992 Toyota Pickup - SOLD

2003 Subaru Forester 2.5X - TOTALLED

2004 Subaru Forester 2.5XT - SOLD

2005 Subaru WRX Sedan - SOLD
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  #11  
Old 03-27-2014, 05:35 PM
capricornbmw capricornbmw is offline
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OP any updates? And zombie if I disconnect a good sensor, is it possible for the engine to still remain normal ? That was not my experience with my afm, but that was my experience with my tps.
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  #12  
Old 03-28-2014, 03:29 PM
E34_Obsession E34_Obsession is offline
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I have done the drivability test with each sensor. I'm probably looking at a bad engine temperature sensor (blue sensor) but not entirely sure yet. Stil investagating.
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1991 BMW E34 525iA

1999 Toyota Tacoma Prerunner Xtracab 2.7L

2008 Toyota Tacoma Prerunner DCSB TRD Sport

1995 Toyota Tacoma 2WD DX V6 - SOLD

1992 Toyota Pickup - SOLD

2003 Subaru Forester 2.5X - TOTALLED

2004 Subaru Forester 2.5XT - SOLD

2005 Subaru WRX Sedan - SOLD
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  #13  
Old 03-28-2014, 08:17 PM
capricornbmw capricornbmw is offline
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Quote:
Originally Posted by E34_Obsession View Post
I have done the drivability test with each sensor. I'm probably looking at a bad engine temperature sensor (blue sensor) but not entirely sure yet. Stil investagating.
Just unplug it and drive for a few days. Your fuel economy won't be perfect (it probably isn't now anyway) but all the problems should be eliminated. Leave nothing else disconnected.

Have you done the stomp test? You probably have, but if you haven't, plug everything back in, delete all codes, drive for about 30 minutes, then do the stomp test.
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