buzzing in engine bay when engine off!!!

[phunt]

hope someone can help....
this problem seems intermittent, when i have been out in my e30 conv. and park up and leave it for a few hours, the battery is flat, now i keep a charged jump battery in the boot just for the occasion... but when i put the jump battery on there is a buzzing that starts, and is coming from the top of the engine!! so i have started to disconnect the battery every time i stop, but sometimes the buzzing is not there and i don't disconnect the battery and the next time i start it its fine...... and other times i've left it connected and its flat, but when i jump it the buzzing starts when jump leads are attached!!... any help will be greatly received, there nothing worse than being in public and you e30 wont start!!!....

[E30BeemerLad]

Sounds like the idle control valve is running constantly (at a guess) although I have no idea why or how to cure it.

[Brianmoooore]

ICV is switched by the DME relay, so the first things to do are to check that the buzzing stops when you pull out this relay, and to carefully listen to the relay while you do it (when the fault is present), to hear if it clicks when you remove and replace it.
Relay is the five pin one (usually white), under the cover by the air filter.

[phunt]

thanks guys, i have taken out the DME relay and the buzzing stops, and starts again when its replaced when the ignitions on... do you know where i can acquire a replacement one?? many thanks again

[Brianmoooore]

carefully listen to the relay while you do it (when the fault is present), to hear if it clicks when you remove and replace it.

What makes you think you need a new one?

[phunt]

if its sticking on then it must need replacing surely???

[phunt]

i have now put the relay back in and it stayed quiet, went back to the car after an hour and it had started making the noise again with the ignition off, so i took the relay out and it clicked as it removed it. when i replaced it, no click and no buzz, until i turn on the ignition, turned off the ignition and the noise stopped!!! can the relay be fixed or replaced??

[Speedtouch]

The relay may possibly be fixed by opening it up and using emery paper/fine wet & dry to clean up the switching contacts, which develop pits and troughs, like the old contact breaker points in distributors used to.

But, you're probably better off getting a new one - should only be a few quid from a BMW dealer.

[phunt]

Thanks guys, i have now sorted it, by replacing the relay with a 30amp/5 pin standard automotive relay (£2.00 from local auto shop) and now as good as new...

[l16ydl]

I've got this, what, has it sorted it out as my mate whos an auto electrician said its a short between the relay and ecu??!!! What relay is it?

[Brianmoooore]

The relay may possibly be fixed by opening it up and using emery paper/fine wet & dry to clean up the switching contacts,

NEVER use emery paper on electrical contacts. Particles of the emery become embedded in the contacts, and will cause arcing. Contacts should only be reshaped by a file.
Nail files are ideal.

[Brianmoooore]

I'm not at all convinced that the fault has been cured! From what you have described it sounds likely that there is a considerable current still flowing through the relay's coil when the ignition is off. Not large enough to draw the relay in, but the sort of current that the relay needs to 'hold' once in.
Pull the relay out, use a piece of wire to connect pin 85 to its correct socket, and connect a meter, on a mA range between pin 86 and its socket. There should be no current recorded with the ignition off.

[l16ydl]

My mate tested it and had a look at some diagrams i downloaded and he said its definately a short some where,he's hopefully going to sort it out tomorrow.