Surging on an M60 engine

Hello,
I got the feeling this is one of those faults that everyone who knows these engines knows about. I have a 3litre M60 engine in my 1993 530i with 106k
miles on the clock.
It seems to have a problem somes when the engine revs down that it'll bounce off the idle point (around 550rpm) and briefly bounce back upto 1200rpm or so, once, before settling down to idle. Its as if the engine controller thinks that the engine is going to stall and tries to recover the situation by blipping the throttle open. Often I can make it do this by manouvering the steering wheel at idle, and somehow the load from the pump just causes it to surge briefly. Other than this i have no problems with engine running at all, other than maybe a slight misfire at idle usually on hot days!
Someone suggested that it might be the idle control stepper motor?
Any ideas definately welcome!
James
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That's one of the classic symptoms of a nikasil engine going bad; about the right number of miles, too. Get a leakdown and compression test. You might read the nikasil problem description pages: http://www.koalamotorsport.com/article-m60v8.asp and http://www.e38.org/nikosil.html#matter
FloydR
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wrote

Thanks for your reply, those links are interesting. I'm not sure about the fuel sulpher content situation in the UK (does anyone else??). I assume its the misfire that prompted your suggestion rather than the surging? Its only very slight, missing occasionally. I've not actually check the casting number to see if I have Nikasil or Alusil block, since 97% of the time it ticks over fine.
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There were problems with the M52 I6 engines in the UK due to (apparently) sulfur in some fuels there. It's a possibility, but something to keep in mind. As the other responder noted, there are other things that could be causing it.
FloydR
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James Bossard wrote:

Yeah, I'd be looking at the idle control valve or maybe a severe intake leak somewehere. Any check engine lights? It doesn't sound like the dreaded "N"-word.
--
-Fred W

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Thanks for your reply. The surging is totally intermittant, usually happens when i come to a stop after putting the clutch down and the revs returning to idle. Also it happens lots when parking and moving the steering it, it feels like the steering pump is causing the revs to drop sub idle and the controller to overcompensating to prevent stall. I had a computer diagnostics done at the last service and nothing came out as unusual (annoyingly). As you say I would not expect it to be a Nikasil issue; more like a strange throttle control problem.
I'm gonna check the idle control valve as I have heard before that these are problematic parts, expensive too :(
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