Xoutpost.com - Overnight Cold Start Rough Idle N62 4.8iS

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Correct, supposed to be 10-15 min job which I'm sure with my OCD it end up being the whole day.

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Quote:

Originally Posted by mr_robot (Post 1147534)

So you replaced the IVM? It's cheap enough and easy enough to swap it seems.
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part number for this IVM/ISM device 12527510638 for years 2003-2006, according to realoem...

12527510638

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In the winter, when its cold out, I've often got the shakes upon startup and then the error on dashboard... so I turn off vehicle and restart adn all is perfect... I spoke with a BMW mech about this and he said just learn to live with it as its not bad actually for the car as it warms up adn problem goes away as opposed to paying for the Lifters replacement.... he never mentioned it could be an IVM/ISM part that could be easily/cheaply replaced...interesting.

Often, a rough idle on a long sitting cold starts is due to slowly leaking injectors. The residual pressure in the fuel rail causes fuel to slowly drip into one of the cylinders. This causes a too rich condition for ignition in the effected cylinders until the extra is blown out the exhaust. Then it smooths out.

You’ll smell unburned gas frm the exhaust on startup.

Diagnosis is to wait for 12 hours, or so, for the condition to set, then pull plugs and see if they are wet. Or stick a wooden pencil in the plug hole and see if it gets fuel on it.

If it's leaking injectors wouldn't it start rough from the start? Also wouldn't it be a consistent cylinder misfiring? But it's random, like today it was only cyl 6. I doubt all my injectors are leaking or I would definitely smell heavy gas which I don't. And I don't think it's technically "misfiring" more like it's slightly retarded because I I rev up slowly to like 1k rpm it doesn't misfire.

And sometimes it does start rough right away sometimes it does the normal high idle (perfectly) and as the rpm settles down (lift being adjusted by valvrtronics) the roughness begins. Again intermittently and random.

Also for me shutting the car off when idling rough and restating doesn't fix it at all and so far this is always been the case. Restarting never does anything. Just have to let it go away on it's own. Have even restarted it 3 times and no chance.

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True. It should idle rough from the start, unless it’s even dripping across all cylinders, which is unlikely.

Anytime I think about problems that show up after extended cold sitting, I think of fuel delivery. Especially since it seems to happen only after the cold of night time.

Fuel starvation for some reason? That would cause lean misfire and the computer to retard ignition to reduce detonation.

Failing return valve in the fuel tank that allows line pressure to drop after the pump shuts off, possibly causing short term initial starvation? Small Frozen glob of water in the fuel tank pickup? Cold causing low voltage to the fuel pump?

Please keep us posted on what you find.

Yeah I looked into fuel supply issues thinking it's losing pressure the longer it sits. First the filter was replaced. Also ran fuel injector cleaners as well just as a maintenance.

To see if it was a pressure issue I primed the pump 3 times before cranking by going starting the key but not cranking on and off so the rails build up pressure but that didn't do anything either.

Also monitored my voltage while this was happening to see if my alternator is failing therefore not supplying enough voltage but it all checked out, voltage goes straight up to 13.8v and does not fluctuate with the rough idle.

So since I finally found about the IVM my really hoping this is it. Because every other potential issues should be happening all the time cold or not warmed up engine or not and it's not the case.

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Welcome to the club!

Quote:

Originally Posted by mr_robot (Post 1147395)

Ok, been trying to diagnose a cold start rough idle I've been experiencing ever since it has been getting cold here in New York.

It has new coil plugs and spark plugs from FCP's ignition service kit about a year ago.

Just got the VSS and all corresponding gaskets including the vanos seals done and at the same time rechecked the spark plugs for any fouling. Everything was good.

DME adaptation was reset after job was done as well. Car drives perfectly normal and strong otherwise.

I'm aware of the intermediate lever SIB and probably it is the issue but just want to understand something.

I get rough idle and sometime the CEL flashing with misfire codes P0300 and random cylinders, sometimes its cyl 2, 4, 6,7 or just 6 or 8, it's never consistent.

With that said it only happens after the car has been sitting over night (over 12 hours) next day going to work.

If it's my I.L. shouldn't it happen all the time for cold starts? For example, after I drive to work and come back (usually 6-7 hours later) it does not show these symptoms. It only seems to happen over a certain amount of time car has been sitting.

So if that is the case it could be a software/setting issue? Like what is different about 6 hours and 12 hours, what changes does the DME make to the valvetronics to go into a certain lift value?

I feel like I can bandaid fix this until I eventually get to do my I.L. if it's something I can change in the settings.

Thanks, any input is appreciated!

Welcome to the club! I've been chasing this since I had mine. Look for a few posts from me on the subject. Initially I discovered the previous owner got fed up and put electrical tape over the bulb (inside so I couldn't see). That was awesome. I've replaced a lot of stuff over the years and nothing has affected it. I also did the IVM because I found a post and diagram on another forum linking the IVM to the levers - no luck. I've also played with all the lift values - no luck. That being said, I did a lot of surgery in recent weeks, it's getting cold and I haven't seen the flashing CEL nor the cold start rough idle. But I've been here before - I'm sure it'll happen :). If mine has the rough start, a restart will cure it.

Noooo! You just killed my hopes lol

But you're saying the replacement IVM didn't cure it but now it's not having cold start issues? So it did cure/help?

Did you take apart the old IVM to see if had any corrosions or faulty soldering?

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