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Discussion Starter #1
Hi all,

I have an odd problem with my 1995 3.8 M5 that noone seems to be able to remedy. It has a bit of a rough tickover as if it's mis-firing. Acceleration smooths out the engine note, but there are definate flat spots and areas of surges in power. It's not really bad, just a little annoying. I have had the plugs replaced, put loads of injector cleaner through and got a guy out to plug a computer in to check the ECU diagnostics for a failing coil and the like and all comes up OK. The throttle bodies all seem to be balanced and the vacuum test come out OK. Any ideas or is it just the nature of the beast?
 

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Dirty AFM?



batmonger said:
Hi all,

I have an odd problem with my 1995 3.8 M5 that noone seems to be able to remedy. It has a bit of a rough tickover as if it's mis-firing. Acceleration smooths out the engine note, but there are definate flat spots and areas of surges in power. It's not really bad, just a little annoying. I have had the plugs replaced, put loads of injector cleaner through and got a guy out to plug a computer in to check the ECU diagnostics for a failing coil and the like and all comes up OK. The throttle bodies all seem to be balanced and the vacuum test come out OK. Any ideas or is it just the nature of the beast?
 

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Dirty, Crankshaft sensor ........... and, you didn't jet wash the engine and there is water down the spark plug recesses?


batmonger said:
Hi all,

I have an odd problem with my 1995 3.8 M5 that noone seems to be able to remedy. It has a bit of a rough tickover as if it's mis-firing. Acceleration smooths out the engine note, but there are definate flat spots and areas of surges in power. It's not really bad, just a little annoying. I have had the plugs replaced, put loads of injector cleaner through and got a guy out to plug a computer in to check the ECU diagnostics for a failing coil and the like and all comes up OK. The throttle bodies all seem to be balanced and the vacuum test come out OK. Any ideas or is it just the nature of the beast?
 

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Agree with the dirty AFM diagnosis, or a split/leak in the rubber boot from the AFM to the plenum, although in my case I did the rest and then a replacement alternator cured my rough idling (more rough than normal and idling at 600rpm).
 

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Discussion Starter #5
Thanks guys, although the terminology leaves me no more in the know than before, hee hee. I'm sure someone will be able to fill me in on what this means and what I can do to clean these bits, once I find them. Thanks again
 

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batmonger said:
Thanks guys, although the terminology leaves me no more in the know than before, hee hee. I'm sure someone will be able to fill me in on what this means and what I can do to clean these bits, once I find them. Thanks again
AFM = AirFlowMeter

Device between airfilterhousing and plenum chamber that measures the cubic amount of air being sucked in.

http://www.realoem.com/bmw/showparts.do?model=HC91&mospid=47387&btnr=13_0340&hg=13&fg=15

If that doesn't work, try cleaning or replacing the TDC sensor. It's the sensor that reads the teeth on the front crankshaft damper.
 

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I thought it was normal for them to have a slightly rough idle as the duration and lift of the cams is quite high. I've always found any car with a powerful engine has a rough idle and it's nothing to worry about
 

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Mine is a little bit rougher now in the cold weather - but its the nature of this engine, some of the reviews of the M5 E34 even mention this when the car is pretty much a new car - a gentle side to side rocking motion, signalling a taste of things to come....(from memory).
 

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I have this problem aswell and I am 90% sure its my MAF thats gone. My MAF has been exposed to the elements quite badly due to the previous owner having a bit of a play with the intake - lets not go there!

Anyway, it could be a your throttle pot, Lamda, your MAF or your crank sensor (covered in crap).

If its MAF its £300 to mr Stealer.

Best thing is to get it down to a specialist and they can see if there are any fault codes like Lambda down etc.
 

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Mine is suffering with this slightly too - only sometimes and it seems more so when it is warming up.
Ill give the MAF a clean and see what happens.
Also checked all the throttle linkage this afternoon too make sure im getting full throttle - turns out the throttle stop was limiting the linkages movement and i wasnt quite hitting full throttle - only 90-95% at a guess....
Quite surprised at this seeing as the car has been maintained by the same BMW specialist for the last 5 years prior to me buying it....
Batmonger - your more than welcome to pop round and i can show you the bits and pieces mentioned


Pete.
 

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lagoonM5 said:
Mine is suffering with this slightly too - only sometimes and it seems more so when it is warming up.
Ill give the MAF a clean and see what happens.
Also checked all the throttle linkage this afternoon too make sure im getting full throttle - turns out the throttle stop was limiting the linkages movement and i wasnt quite hitting full throttle - only 90-95% at a guess....
Quite surprised at this seeing as the car has been maintained by the same BMW specialist for the last 5 years prior to me buying it....
Batmonger - your more than welcome to pop round and i can show you the bits and pieces mentioned


Pete.
Did you take off the plenum to measure this? Otherwise your butterflies are now passing beyond full throttle and closing up again. 20.7mm is the value if memory serves me correct.....
 

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Discussion Starter #13
Sounds good. Getting confused with all this terminology. My number's 07799 694525. Give us a shout sometime.



lagoonM5 said:
Mine is suffering with this slightly too - only sometimes and it seems more so when it is warming up.
Ill give the MAF a clean and see what happens.
Also checked all the throttle linkage this afternoon too make sure im getting full throttle - turns out the throttle stop was limiting the linkages movement and i wasnt quite hitting full throttle - only 90-95% at a guess....
Quite surprised at this seeing as the car has been maintained by the same BMW specialist for the last 5 years prior to me buying it....
Batmonger - your more than welcome to pop round and i can show you the bits and pieces mentioned


Pete.
 

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Stevie said:
Did you take off the plenum to measure this? Otherwise your butterflies are now passing beyond full throttle and closing up again. 20.7mm is the value if memory serves me correct.....
Not sure if were talking about adjusting the same part of the throttle linkage.
Due to wear in the primary linkage that the throttle cable pulls against there is a small bar that then operates directly onto the throttle bar that opens the 6 throttle bodies - the small actuating arm that links the primary throttle mechanism to the throttle bar that operates the bodies directly has worn at both ends where the pivot points are so much so that throttle movement is restricted.
I havent adjusted the rod length on each throttle body merely reduced a small amount of play in the linkage.
Does this answer your question or am i barking up the wrong tree

Any info measurements you have to setting up the throttle id gladly have but the car feels alot better for it already:wroom:

Pete.
 
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