Difficult to drive at low speed - The Unofficial BMW M5 Messageboard (m5board.com)

ilundber · 21st April 2005, 15:37

I have had this problem for ages but it hasen't bothered me very much until now.
The symptom is that when driving at low speed (20 -40 Km/h) and releasing the accelerator is cuts down to zero at once. There is a "thump" in the car and it is as if someone pulled the car backwords. Accelerating gently gives the same result, only the reverse. It takes of with a "kick" and a "thump". This is getting anoying. Besides, I believe that this will wear the transmission parts prematurely.
Should I adjust the intake butterflies to a allow for a small amount of air to enter that way even at idle or what should I do? I think the butterflies close completely now, but I have never touched them so I don't know the proper setting.

Any other ideas?

Cheers!

IvanDias · 21st April 2005, 17:20

If there is a good "thunk", then check the rear axle beam bushes.

If you mean the engine itself, then this I think is fairly normal. For instance, a little game; Try sitting parked somewhere, in neutral, then press the accelarator to go from idle (850ish rpm) to exactly 1000rpm, the first white line.....

Can`t be done. You add more and more pressure to the mechanical cable, but there are six throttle bodies, one per cylinder, which is normal only on bikes and M-Cars, so the cable doesn`t move. Suddenly you have enough pressure to open all six, and the revs jump to 1100+.

Try it the other way is easier, drop the revs slowly to 1000rpm, this is sometimes do-able.

That is why driving the M5 smoothly at low speed around town or in a traffic jam is a talent. The mechanical nature of the throttle system does cause those clunks and jerks when coming off and on the throttle lightly at low speed.

Sometimes I get a "harmonic", especially at very low speed in first, for example in a traffic jam at walking pace, where the car "bounces" forward and back as the play in the gearbox and transmission argues with the car trying to be on and off the idle at 900-1000rpm.

Then again, my car just might be knackered!!! LOL

Ivan.

ilundber · 21st April 2005, 17:24

OK. You just described my car and the driving experience in slow traffic

I understand that I need to improve my slow driving talent

Mvh /Ian

M5Sime · 22nd April 2005, 12:20

I think I would agree with you as this is what I have just noticed buying my LE. There is gearbox play, mine has dual mass/gearbox ratlles on idle and also the throttle is a pain to mudulate smoothly (my previous E39M5 was drive by wire!)

I also notice slightly uneven power at 2-3k - when cruising on the motorway with light throttle and 80 say, you can just feel a little 'tugging' as the engine runs slightly lumpy.

Bit more power on some strokes I guess?

I am putting this all to the 'analogue' nature of this fat 3.8 six.

Cheers

Pepsmeister · 22nd April 2005, 15:31

Don´t you just love it!!

I get the same gearbox, throttle position conflicts, especially when the engine is still cold. I can also feel those slight tugs when cruising at low speed.

It´s the "M" division´s way of reminding you that there´s a racing engine under the hood

WylM5 · 22nd April 2005, 16:59

Ivan's first reply that the rear bushes are worn are probably correct. Considering the age of our cars and the fact that probably none of them have had the labor intensive job of changing rear bushes done. I hope to have mine done soon so that "thunk" goes away for another 10 years.

Hey Ivan! I'm glad to know I'm not the only one that has a "bobble" head when driving slow and not paying attention! LOL!

M5Sime · 22nd April 2005, 17:07

Quote:

Originally Posted by WylM5

I hope to have mine done soon so that "thunk" goes away for another 10 years.

LOL!

I think it might be something else as mine just had new rear subframe bushes. Driveline play and lumpy engines.

Hoping to trace the clonks on low speed bumps and sleeping policemen...

DrSakke · 22nd April 2005, 17:41

Quote:

Originally Posted by M5Sime

I think it might be something else as mine just had new rear subframe bushes. Driveline play and lumpy engines.

Hoping to trace the clonks on low speed bumps and sleeping policemen...

Odd...
I have always thought that my M5 touring -93 was easy to drive at low speeds and very easy to modulate the throttle.....Maybe my car is faulty?

(well it is now with busted timing cahin tensioner etc....)
My girlfriend trained for the drivers license with it summer AND winter(snow etc) and she always liked driving the M5 better that Golfs etc as it was so easy to drive....

Sakke

Cyrus · 23rd April 2005, 10:06

Sounds like alot of people have this uneven driving drving problem at low speeds.

Low speed cruising lumpiness at a constant speed is so annoying and I have been trying to fix it for ages. Cleaning the crank sensor made a bit of a difference but seems like it needs a better clean. The car should not do this and its is 100% a problem. Feels like an airleak somewhere.

I will find this problem.

ilundber · 25th April 2005, 11:50

All,

I did have a look under the hood during the weekend. I found that when you gently move the accelerator set-up by hand directly on the engine (engine shout down) you hear a tiny "click". I loctaed it to the fuel opening valve at the very front of fuel line tunning across the top of the engine. It seems to match the throttle position where I get the very abrupt acceration/deacceleration. It is actuated by the axle that runs through the air inlet tubes.
I will contact an M5 specialist and find out how the butterflies shall be set in order to aviod this if possible.
I'll keep you posted.

Cheers.

By the way, I just learnt that I will get a new engine for my E39 M5 since the old engine can't be repaired. Water has entered several cylinders and scrateched. I hope to have the car back in a couple of weeks. I am lucky to have the old E34 since I need a reliable car even though I had to replace the alternator three weeks ago