BMW 5 series rough idle - J.B.
I have an old shape 520i (6 cylinder). After starting it from hot or cold it normally idles perfectly, but if I start it from cold and stop it again before the water temp rises, then the next time I start it, it runs really roughly for about two mins, like its only firing on 4 or 5 cyls. It does not matter whether the restart is a few minutes later or a few days.There are no other symptoms. Auto choke/ airflow meter spring to mind but I dont know much about the workings. Any brains out there?
BMW 5 series rough idle - David Davies
One possible answer to this is that you have one or more sticking valves.First thing to check is the valve clearances-they should all be 0.010" cold.You could also try adding something like Forte Gas Treatment to the fuel.Of course there could be many other causes of this problem,but as always check the basics first.
David Davies (Tune-Up Raglan)
BMW 5 series rough idle - kal
could it be a faulty temp sensor, as the car warms up may be the fuel enrichment comes of to quickly. How does it drive and accelerate when fully warm.

Do the usual checks of plugs, leads, air filter and check fuel quality.
BMW 5 series rough idle - J.B.
Yes it sounds like no choke or something but why only under the circumstances I outlined?. At all other times including normal hot or cold starts it runs like a dream. Only after being shut down before the water temp rises, and started again either then or later does it happen.I think it's too regular and peculiar to be a sticking valve, but I might try some goop just incase.
Thanks for the thoughts.
BMW 5 series rough idle - Dude - {P}
This sounds very much to me that the fuel enrichment control required for start up from cold, is still operating when the engine is prematurely switched off, so that when you restart, the engine will be too rich, and not run properly until the excess fuel has been burnt off. This is not a fault with the car, but the way you are operating it, and will occur with any modern vehicle with an ECU.
BMW 5 series rough idle - Aprilia
I think Dude is right. This is common on a lot of cars. Some (e.g. Nissan) enable you to implement and 'anti-flooding' routine - you hold the throttle wide open whilst starting and it reduces the amount of fuel injected to as to help clear the engine.
BMW 5 series rough idle - J.B.
Sounds good to me. I'll have a go tomorrow and let you know thanks.
BMW 5 series rough idle - eMBe {P}
Re the mention of similar problems on Nissans, look up

www.honestjohn.co.uk/forum/post/index.htm?v=i&t=24...5
and
www.honestjohn.co.uk/forum/post/index.htm?v=i&t=79...1
BMW 5 series rough idle - J.B.
I started it last night and shut it down after one minute. This morning I tried your technique but it would not go at all. I very nearly flattened the battery but eventually using no throttle it started in the usual rough manner and is now OK 'til next time. The handbook says not to touch the throttle except if it wont start when hot so i'll just avoid the scenario unless someone else can think of something. Thanks for the thoughts.
BMW 5 series rough idle - Dude - {P}
This is most certainly not what I was referring to in my earlier thread, - it is imperative that the car is allowed to complete the cold start cycle (i.e. it must reach it`s full operating temperature) before turning the engine off, so that the ECU switches out of the fuel enrichment mode, and the engine does not become flooded, as would have occurred after just 1 minute. I repeat that there is not a fault with your car, but the way you are operating it.
BMW 5 series rough idle - J.B.
Thanks for your comments Dude but are you saying that i'm at fault by getting the car out of the garage to wash it and turning the engine of before i do so. Pretty crumby system if it wont cope with a restart when I want to put it away. Or am I missing something here?
BMW 5 series rough idle - Aprilia
Unfortunately this is the way the system operates. My 7-series with Motronic was the same.

My wife's Nissan is better because when you hold the throttle open it cuts the fuel and so clears the engine - fires up easy!
BMW 5 series rough idle - eMBe {P}
but are you saying that i'm at fault by getting the car out of the garage to wash it and turning the engine of before i do so. Pretty crumby system if it wont cope with a restart when I want to put it away. Or am I missing something here?>>


Yeah, Dude is right. These ECU systems were designed before the geeks realised that not everyone starts their car to drive a reasonable distance before switching off the engine. Read the posts in the links I posted above for confirmation.
BMW 5 series rough idle - Andrew Moorey (Tune-Up)
There is some feeling that the problem is caused by bore wash- the excessive fuel washes away the oil from the bores and you have a lack of compression. The way round it is to leave it running for a few minutes to get some heat into the engine. This way you will avoid the horrific wear you are subjecting the engine to by washing the oil out of the bores.
Andrew



Simplicate and add lightness!
BMW 5 series rough idle - Dude - {P}
JB can you confirm if your car is now starting OK, if you bring it up to operating temperature before switching the engine off ???
BMW 5 series rough idle - Dizzy {P}
Dude,

I think your mention of bringing the engine up to operating temperature could mislead others into thinking that the engine has to be run until it is warmed right through.

I'm sure you agree that the engine needs to be run only until the 'fast idle' drops to 'normal idle'. This time of year probably just a couple of minutes is enough.

As a rule I let my BMW 5-Series engine run until the idle speed drops but I have occasionally switched off almost immediately after starting without any problem. Therefore, like yourself, I would be interested to know if letting the engine run for a few minutes before switch-off cures JB's restart problem.
BMW 5 series rough idle - J.B.
Sorry this is a bit late, I've been away. Yes the car is perfect as long as I don't do what we've been talking about. I'm grateful for all the comments and never thought BM would allow such a rubbish system to get through to the public. I'd be really interested to know how many it affects. Presumably there isn't a fix if its an ECU problem (apart from being separated from shed loads of the folding stuff that is.)Just to fill in the blanks i've not noticed that it runs at an enhanced idle when in the warm up phase but it is true that once the temp gauge registers it is ok to shut it off if necessary so a few mins in summer is about right.
BMW 5 series rough idle - Dizzy {P}
J.B.

I'm pleased you've found the answer, even if you aren't happy that it happens.

What I don't understand is why my own BMW has never given the problem. Mine is a 1992 E34 with the 2.5 litre M50 engine (24 valve, chain-driven camshafts). Is yours older/newer than mine?
BMW 5 series rough idle - J.B.
mine is a 95M 520 (shape before the current one) 24V not sure about M50 etc
BMW 5 series rough idle - Dizzy {P}
Yes, yours will be the M50 as well. Perhaps the increasingly tighter emissions regulations forced a change on the later ECUs but it does seem a backward step if it introduced the problem that you and many others are now facing.

On the other hand, as others have said, letting the engine run for a few minutes is good for engine life!
BMW 5 series rough idle - jud
At last a comment other than the dubious comments previously, i regularly start my car and move it out of the garage to wash it or just to get something from the garage its self. That takes a very short time perhaps 90 secs?. I have had two primeras and now the A4, and never had a starting problem afterwards (or with any other car)just let the revs drop to a fast idle before turning off. To say you have to warm a engine before turning of is just not true.
BMW 5 series rough idle - harry m
i had a n reg escort l.6lx and used to have to wait for it to idle normally otherwise it would either not start or misfire when next trying to start it.
BMW 5 series rough idle - Aprilia
Jud

Your comment is the dubious one, mate. Different cars have different engine management systems and behave differently (unsurprisingly).

Nissan, for example, had exactly this problem with the old Micra. They even went as far as supplying a modified wiring harness to the coolant temp sensor to get around the 'characteristic' by changing the engine temp. value reported to the ECU.
The Primera is a different system again (much better). Some BMW's DO suffer this problem - I had one; the answer is to let the engine run a bit until its out of its 'cold start enrichment' phase. How long this takes depends on both engine and ambient temperatures. Obviously it takes longer during the winter.
BMW 5 series rough idle - Dizzy {P}
Some BMW's DO suffer this problem - I had one; the answer is to let the engine run a bit until its out of its 'cold start enrichment' phase.

>>

Aprilia, this is exactly what I meant -- and in fairness to Jud, I think he meant the same.

Incidentally, I have been quite impressed with the technical answers you have been contributing to this forum over the past weeks, on auto boxes etc. I tried to read your profile but alas nothing comes up. Any chance of telling us a bit about your background?
BMW 5 series rough idle - hispecgolfs
last warning about your username & sign-off.

Don\'t use it unless HJ has approved it.

Mark.

 

Value my car