e34 525i auto - problems starting from cold - BMW Forum

Mr-Dee · 02-25-2010, 03:30 PM

Hi all, I have had a good look through the forums but I cannot seem to find a similar problem listed so I thought I would open this thread

It is now difficult to start from cold, fine when warm, from cold I have to give plenty of throttle and it kind of struggles to fire, its very lumpy as if it is not firing on all 6 cylinders, I have to fight with the accelerator peddle to keep it going, after a few seconds or so of doing this keeping the revs up it is fine, if I try to just start it normally it just dies instantly. It has started doing this after having my car back from having some MOT work, the reason I mention this is because it had some welding done on the exhaust system and when I had the car back I did not have to reset my stereo settings etc so it is obvious that the battery had not been disconnected while being welded and I am just wondering if this could have damaged something like the ECU or something ? or a sensor somewhere ? or maybe it is just coincidence ?

Your advice would be very much appreciated, as we all know the Haynes manual for this model is not the best to say the least hehe and I was wondering if someone could list the things to check first as I am sure there is probably a sequence of things to check and/or most probable cause

Thanks :-)

marti5 · 02-26-2010, 03:15 AM

I would get a diagnostic done, it could be down to an o2 sensor....or the MAF/AFM

Coug51 · 03-21-2010, 01:52 PM

I am not an expert on this, but I also have similar cold starting problems and it was improved a lot by getting my engine decarbonized. How many miles does your engine have? After 255,000 miles, my engine had carbon build up, which acts like a sponge and soaks up moisture and/fuel. My mechanic noticed the carbon deposits and start up greatly improved after one treatment; but it still is a bit of a problem and he had recommended I do it again after three months pass. Also, one long car trip helped the starting problem some--which helped to blow out more carbon. My 1989 e34 took short 2 miles commutes, so the engine didn't have the opportunity to clean itself out very well over many years. Hope this helps. The decarbonization cost me about $120.

Mr-Dee · 03-21-2010, 02:11 PM

Cool ;-) It may be worth me getting the engine de-carbonised anyways in that case, yeah mine has done similar miles but still seems to be going strong :-) getting general advice like this is so needed as these cars get older, but that is why we joined this excellent forum :-)

darkhorse737 · 03-21-2010, 04:42 PM

Quote:

Originally Posted by Mr-Dee

Cool ;-) It may be worth me getting the engine de-carbonised anyways in that case, yeah mine has done similar miles but still seems to be going strong :-) getting general advice like this is so needed as these cars get older, but that is why we joined this excellent forum :-)

when was your last tune-up?

If it was like eons ago... i would say do a tune-up first and see.

If tune-up done recently... then i would start by testing the ECT sensor. That would be the sensor that determines driveability of bimmers in cold start vis-a-vis warm start operations

Coug51 · 03-22-2010, 04:06 PM

Yes, I totally agree with Darkhorse that you should check other things first before decarbonizing. In my case, the e34 just had a complete tune up, brand new injectors (X6) installed, and a new thermostat. Also, for good measure, the motor control unit (computer) had to be replaced because the output signal was not quite right. The air mass box was okay, as was the O2 sensor. About the only other thing we didn't check, and that is sometimes associated with cold weather start problems, is the cam position sensor. After these repairs and checks, there was still a cold starting problem and no problems once the engine warmed up, so my mechanic suggested sending it out for decarbonization. And as I stated earlier, it helped a lot. In my amateur search of the web, cold start problems can also be related to the spark coils (oil can seep into them if there is an oil leak from the top end). Some earlier model cars also had some kind of a cold start sensor or relay of some kind (ECT sensor??) but I didn't pay attention to it because that part didn't apply to my model. Good luck!