Misbehaving 525

[Emile]

I need some assistance. During the past 3 or 4 months my 1996 525i M50 manual started misbehaving on occasion during take off from 1 st gear – the revs will increase like normal but the car will just not accelerate as usual, and there is a slight vibration like the clutch is slipping but no shutter or any noises. I’m not a mechanic and every time someone else drives the car this will not happen and then they don’t know what look for. The car was at BMW and apparently there is no fault codes stored – they say maybe I should replace the airflow sensor but they don’t know for sure because when they had the car this problem obviously didn’t occur and to just replace something I think is a wast of money if it’s not solving anything.

I bought the car second hand and currently there’s a bit over 200000km on the clock. I recently (15000km ago) replaced the clutch kit and the slave cylinder. I don’t know if the o2 sensors have ever been replaced.

Otherwise the car is going fine except for a small steering wheel vibration when braking at high speed say at 120 – 130km/h. I first replaced all four brake disks (do not know what the correct description is) and thereafter the lower control arms and a month ago the thrust arm bushings – all of these improved the vibration but it is still not totally eliminated and it is starting to irritate me as bit. Can this be tire related – I fitted 2 new rear tires a while ago due to a piece of scrap metal that ruined one tire on the highway. The 2 front tires are like new and I had all four tire balances and alignment done – so what else can be done?

I would appreciate some comments or advice – I like this car but at stages I just feel like selling due to little things that no one really seems to know how to solve even BMW.

Emile
SA 1996 E34 525i manual 200000km

[George M]

Emile,
If your suspension, tires/wheels, rotors etc are in good condition and you are getting a shimmy during high speed braking than a possible cause is runnout between your rotors and wheels. You didn't state where you are from but since posting in km and fluent in English presume you are from Canada with harsh winters and corrosion can build up behind wheels causing runnout of the wheels relative to your newish rotors.
You need to remove the wheels and wire brush the back sides so they mount flush to your rotors/hubs. Thrust arm ball joints and bushings are perhaps the biggest player in high speed shimmy under braking.

As to your driveability issue, since no codes and an intermittent issue, you won't get a good arm chair tell from the web as enlightened as this board is :-) With an issue such as yours if you are mechanical...the dealer will rarely be any help...sometimes no help if the issue is blatant ;-)...you need to get a Bentley manual and start working through the engine. This does not take long. Start at the front of the engine and work back, checking all the engine management sensors...starting at the CPS. Your driveability issue could be anything...perhaps a bad ignition wire...a fuel pump on the way out...any one of the sensors etc....dirty throttle body...vacuum leak from any one of the hoses or throttle body bellows etc. All of this is pretty easy to diagnose but you have to sweat the details if you want to find your intermittent issue.
Good Luck.