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From digest.v7.n568 Mon Nov 10 20:26:22 1997
From: "Max Dufford" <>
Date: Mon, 10 Nov 1997 13:55:23 -0800
Subject: Re: 97 M3 Idle, and More

>Sometimes when starting the car stone cold (in the morning), I experience
>a brief metallic rattling that is very disconcerting; the dealer advises
>that this is normal - the hydraulic lifters and/or cam chain tensioner
> bleed down overnight. The rattle vanishes within a few seconds; and,
>there are no ticking or unusual sounds after (until the next time). Anyone
>with some experience or information in this regard?

My 97 M3 does this from time to time. I had convinced myself that it was probably just another oil starvation problem inherent to these engine, I hear the sound more like a dry bearing. The chain tensioner could be a good candidate, but I pinned the sound to emanating from the vanos unit. After a few seconds when the oil presure goes up its gone. It's very intermitent, doesn't happen on every cold start. Whatever it is it will go at some point, metal on metal even for a few seconds will eventually cause a falure.

The first time it happened I was far from home, so I enquired a few days later to the Las Vegas BMW dealership Service rep for any knowledge of this sound or related oil starvation problems. He told me that there were no problems with these engines. I ask them about about our not so favorite lifter noises and he told me that only happens when you go too fast around corners!

>Maybe they all really do idle poorly

The idle does stumble alot. I find that when that silly air pump (the one that blows air into the exhaust manifold/ports) is on it's really bad. I know this is one of those "essential emission controls" but the lightweights I've seen don't have them, what gives? I may just rip it off some evening and see if this improves things. We took one off a friends 993 motor (w/ OBDII) and it didn't hurt a thing. He even scored zero emmisions on CO and Hydrocarbons, not bad for a 79 SC.

Thankfully no catalyst problems yet. Just put over 5000 miles on it during a long vacation throughout the west with no major ills, lots of driving at autobaun speeds and no tickets. After returning home I took a sizable piece of metalic road debris in the windshield/roofline, blew glass clear into the backseat. Now will see if you can match soft Techno-violet paint.

Max Dufford
'97 M3

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