erratic tickover and speedo with mind of its own

[MICKEY2311]

hi, my 325i cabby runs very erratic on tickover , like its surging . I'm no mechanic but any ideas would be appreciated . Also my speedo seems to have a mind of its own , when i ease off the throttle to change gear , the dial dips to zero until i have pressed the throttle again . Any ideas anybody ? cheers

[pianist]

Coud be a few things with this so I'll start with obvious one first: if you had your battery disconnected for a period your ecu has to learn some things again and some times you get this rpm dip after you push and let go accelerator and eratic running sometimes is cause while it is learning the engine is running in very low rpm, usualy after few runs or days it cures it self.
Now do you get the dip in rpm sort of like choking while pressing the accelerator cause this could mean something is wrong with your ignition timing.

[Speedtouch]

Try disconnecting either battery or ECU, leave for an hour to reset, then let the engine idle for at least 10 minutes to enable base idle setting to be learnt, switch off, then go for a drive throughout the rev range.

Faltering speedo may be a loose connection to the sensor on the diff, so check that's on properly.

Do your service indicator lights work? If not, duff batteries may be affecting the instruments, but they are fairly easy to replace.

[MICKEY2311]

The battery hasnt been disconnected at all for a long while now . The car drives sweet ,its just on tickover where theres the issue . Ive owned it for two years now and its always been like it , but it shouldnt be ,so i want it sorting . Maybe im being a pain but just want it right if you know what i mean .
Will check sensor connection at diff
Battery only a year old so doubt that is the problem , but as i say im no mechanic.

[MICKEY2311]

I like the sound of one of your chips , will this also sort out my tickover problem ?

[Speedtouch]

PM sent!

[pianist]

Did you try this:

http://www.pelicanparts.com/bmw/techart ... ooting.htm

[pianist]

When I used to have 323i I had a problem with idle jumping up and down which is very common in all m20 and after I changed Idle Control Valve (ICV) it was back to normal. Just another thought

[BATTS91]

The batteries speedtouch is reffuring to are in the intrument cluster itself not your big battery under bonnet , also what has been already said is the connections to the diff for the speedo if it has the original white plug conector take it off spary some wd40 and give a wiggle about and if not get some female connections and chop the lig off and use them instead

[MICKEY2311]

ah i see , i wasnt aware thar there were batteries in the instrument cluster . doh ! are the replacements readilly available and if so , where from ? thanks for all the help and advice

[Speedtouch]

Yes, they are available from the likes of Maplin, Farnell, RS, CPC, etc.

You ideally need the ones with solder tags, but it is possible to re-use the ones from the original batteries (assuming yours are the AA type Ni-Cd; later ones used small Lithium batteries).