325i surging idle problem, im so stuck:(

Post Thu Nov 15, 2012 5:56 pm

Hi i have a problem with my 325i convertible 1991 and would really appreciate any help!
It was running fine last year but i removed the battery and left her standing on the drive since then as i worked abroad the past year. A few weeks ago i put a new battery on an started it up but it was surging on idle, revving beetween 1k and 2k revs constantly, but would rev up fine when applying the throttle.
Iv let it run upto temperature, iv taken it for a drive, iv replaced the idle control valve twice (as they were used items), i really cannot see that any hoses/pipes are leaking, and in doing all these theres been no difference, i changed the air flow meter today and its still the same but now just revving from 1k to 1 and 1600k. Also since this problem started everytime iv pulled the plug off the idle control valve it has made no difference to the idle at all? One other thing i have noticed is that every now and then i start it and instead of it constantly revving up an down it idles very rough at about 700rpm! the complete opposite! but this has only happened about 1 in every 20 times iv started it, an once iv revved it she starts surging again as described.
Please please if anyone has any suggestions or help for me it would be very much appeciated,
Thanks, Ben

Post Thu Nov 15, 2012 6:55 pm

After diconnecting the battery for such a long time, the ECU needs to "Relearn".

Take it for a drive, about 30-40 minutes, various styles of driving......

Post Thu Nov 15, 2012 7:00 pm

Ah thanks mate, i did hear something about that so i took it out for about 20 mins of driving, mostly sensible but then i did give her a few bootfulls here and there. Would u not say that was for long enough really?

Post Thu Nov 15, 2012 7:34 pm

i would say around 30 mins should be enough, but you need to make sure that you do take the engine to the limit of the rev range a few times, when warmed up.

If this dose not solve the problem, youll need to check the TPS under the throttle body, it may of gotten gummed up.

Post Thu Nov 15, 2012 7:40 pm

When you reconnect the battery let the car idle for 10mins then shut it off, restart then drive for 30 - 40mins throughout the rev range.

also as kam says check the TPS switch under the TB, if it's full of crap clean it out & also check the round plug/connecter hanging down uder the TPS/TB as that to can become full of crud.

also to check for any air leaks, even tiny one's spray some wd40 around the TB, inlet manifold area, if the engine note changes then you've got an air leak.

Post Thu Nov 15, 2012 7:44 pm

Thanks guys, il try all this and let you know how i got on. Thanks again

Post Fri Nov 16, 2012 10:17 am

steve_k wrote:When you reconnect the battery let the car idle for 10mins then shut it off, restart then drive for 30 - 40mins throughout the rev range.

also as kam says check the TPS switch under the TB, if it's full of crap clean it out & also check the round plug/connecter hanging down uder the TPS/TB as that to can become full of crud.

also to check for any air leaks, even tiny one's spray some wd40 around the TB, inlet manifold area, if the engine note changes then you've got an air leak.

^^^^^

Defo check for air leaks and the TPS switch - that gets my vote!

Post Fri Nov 16, 2012 10:25 am

If the TPS switch is full of crap (oil) then take the TB & drill a 1mm hole in the bottom of the TPS switch to allow any oil to drain out.

Post Sat Jan 12, 2013 5:15 pm

Since my last post iv had to wait till I finished the work I was doing like brakes an other bits and then get her mot'd taxed and insured before taking for a drive that long (re-learn ecu) Iv taken it out today for a bit, not long enough as suggested because it is very horrible to drive, it jolts an cuts power about every ten-twenty seconds when just cruising along in like mid range of the gears, it even backfired once, It did a similar thing a couple years ago when the flywheel sensor went, but then it didn't have an idle surging problem too. Do you think I maybe need to change the flywheel sensor again? Or does anyone have any other suggestions as too what it may be?
Any help would be very appreciated, thankyou

Post Sat Jan 12, 2013 5:29 pm

A 1991 325i shouldn't have a flywheel sensor - these were only fitted to pre-facelift chrome bumper 325i's on C to E-registrations!

It could be a loose electrical connection - check the engine to body earth strap, and all wires around the ignition coil.

Also check the DME (Main) relay, the 5-pin one, usually white, in the black block near the header tank on the nearside front wing.

Post Sat Jan 12, 2013 5:58 pm

Rotor arm and dizzy cap spring to mind,H/T leads all plugged in properly?

'Flywheel sensor' does sound a bit strange,although cabbie's do tend to bit a bit different to saloon,this sensor should be mounted at the front of the engine on the exhaust side reading a toothed wheel mounted behind the lower crank pulley.

Post Sat Jan 12, 2013 9:17 pm

Well it was originally a 320, I bought it because it was so clean and at the time I was getting fed up with all the 'mint' 325's I looked at turning out to be rotboxes! So I changed the engine to a 2.5 from a 90k automatic tourer in the second week of owning it, obviously keeping mine manual etc. but I thought it was still a late engine, maybe I'm wrong tho I don't know? Rotor arm, dizzy, leads an plugs are all brand new. And yeh it does have the sensor you've explained on the toothed wheel. I will have a look at the earth strap and main relay tomorrow cheers. If it helps.. The car ran perfectly before I left it on my drive for most the year as I said on my first post. I'm just so confused with it now and really am thankful of the help n suggestions u are all giving me, cheers

Post Sat Jan 12, 2013 9:41 pm

Try disconnecting either the battery or ECU for an hour or so, reconnect, then let it idle for at least 10 minutes to enable base idle settings to be learnt, then switch off, then take it for a drive throughout the rev range.

This ensures full transfer of the EPROM data into the ECU processor.

Post Sun Jan 13, 2013 10:07 am

BeemerBen84 wrote:Well it was originally a 320, I bought it because it was so clean and at the time I was getting fed up with all the 'mint' 325's I looked at turning out to be rotboxes! So I changed the engine to a 2.5 from a 90k automatic tourer in the second week of owning it, obviously keeping mine manual etc. but I thought it was still a late engine, maybe I'm wrong tho I don't know? Rotor arm, dizzy, leads an plugs are all brand new. And yeh it does have the sensor you've explained on the toothed wheel. I will have a look at the earth strap and main relay tomorrow cheers. If it helps.. The car ran perfectly before I left it on my drive for most the year as I said on my first post. I'm just so confused with it now and really am thankful of the help n suggestions u are all giving me, cheers

Throttle position switch(TPS)would be my next port of call.As already written,it needs checking for correct operation,and perhaps letting the oil drain out of it.
Check that you can hear it click as soon as you move the throttle butterfly,remove the rubber 'bellows' and see if the breather system has left oil in the T/B,this is a decent clue to the TPS getting gummed up with the stuff.

Post Mon Jan 14, 2013 11:40 pm

Thanks guys, soon as the snows disappeared I'm gunna do the tps, and check the other things mentioned. Also 'speedtouch' iv just realised you live about 2 minutes round the corner from me (ps that's not a come an help me haha, I'm just sayin as I noticed it haha)

Post Tue Jan 15, 2013 2:44 am

There's a plug that connects the injectors to the main loom under the intake manifold, it's a small black round thing looks like a smaller version of the c101 plug next to the fuse box.
Trying giving that a wiggle quite firmly where the rubber joins to it at the top and bottom when it's idling, if it changes revs then could well have corrosion in there so open it up to check (just twists open), if it doesn't look too bad just spray with some contact cleaner and put it back together.

Post Tue Jan 15, 2013 1:42 pm

Green wrote:There's a plug that connects the injectors to the main loom under the intake manifold, it's a small black round thing looks like a smaller version of the c101 plug next to the fuse box.
Trying giving that a wiggle quite firmly where the rubber joins to it at the top and bottom when it's idling, if it changes revs then could well have corrosion in there so open it up to check (just twists open), if it doesn't look too bad just spray with some contact cleaner and put it back together.

Wise words, given its been standing the injectors may be gummed up. mine was idling like a sick dog (also a cabby that comes out during the week we call summer!)and i have just stipped and replaced the injectors with used ones that were prof cleaned and its sorted all the idel problems out.

Post Tue Jan 15, 2013 1:48 pm

PM sent.

Post Sat Feb 02, 2013 7:36 pm

WOOOO!!

She's fixed and running perfectly again. I tryed absolutely everything above and it turned out the problem was faulty ecu. Put another one in today and she's fine now

In fact it's actually better than before, feels alot more responsive etc than its ever been.
Thankyou to everyone for your help an suggestions, very much appreciated