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Discussion Starter #1 (Edited)
Hi all.

My M5 has recently developed a very rough idle only when the engine is cold and not fully warm. Initially when it began happening I found that the 2 breather hoses in front of engine bay were completely deteriorated with holes and tears in them (which is common) so I replaced them hoping this would solve my problem, but it didn't.

So today I decided to take a video (below) showing the rough idle and then pumped the brake pedal a few times until the engine stalled for the first time since I developed this problem. I have had a full straight pipe setup with evolve 4-1 headers, decats, x pipe and muffler delete on my car for nearly 1 year now without any problem, along with the evolve alpha N MAF-delete tune. My car is healthy and even with this rough idle, once the engine is warm I have zero loss of power and my car pulls a strong 450BHP. I have no CEL or dash warnings. Any suggestions would be appreciated. Thank you.

<iframe width="560" height="315" src="//www.youtube.com/embed/mniOo1B28VE" frameborder="0" allowfullscreen></iframe>
 

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Any suggestions guys?
OK, I'll play!!

Perhaps an air or vacuum leak that seals itself when the part causing the leak expands with heat?

Also, when you are on cold start, no O2, you are open loop. When warmed up, you are closed loop, so the O2 is giving feedback and the car is compensating for whatever the issue is.

Hope that is food for thought.

Regards,
Jerry
 

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Discussion Starter #4
Thanks for the reply. Further bad news. I now have the very very rough idle even when my car is fully warm! I've just driven around for over 1 hour, and to my shock, this is the first time that this problem has occurred once my car is fully warm. My car even stalled when stationary without pumping brake pedal! It's becoming undriveable. Still no loss of power though anything above 3000RPM. Help :sad1:
 

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Still no codes?

As Jerry mentioned, check for vacuum leak.

Any work done that required the air intakes to be removed? If so, make sure it was put on properly and isn't loose or there aren't any gaps allowing air in.

When was the last time the fuel filter and or fuel pump was changed? Can you check fuel pressure?
 

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There are many codes that do not light the CEL. You need to check for codes. Doesn't Evolve have a free download that can read them?
 

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Discussion Starter #8 (Edited)
Still no codes?

As Jerry mentioned, check for vacuum leak.

Any work done that required the air intakes to be removed? If so, make sure it was put on properly and isn't loose or there aren't any gaps allowing air in.

When was the last time the fuel filter and or fuel pump was changed? Can you check fuel pressure?
Fuel pump and fuel filter were changed under a year ago. The air intakes haven't been touched since the evolve headers were fitted 1 year ago. Are the air intakes the 2 big plastic tubes that go into the top of engine?

I need to get over to a garage to get the codes read then.

Also how do I check for vacuum leaks?
 

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Discussion Starter #9
There are many codes that do not light the CEL. You need to check for codes. Doesn't Evolve have a free download that can read them?
No I haven't got the evolve tuning cable as I went into their HQ to get all my work done. Will have to go somewhere local to get diagnostic done.
 

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Top two guesses for vacuum leaks (without codes...) would be the plastic elbow connecting the idle control valve hoses, and/or the hose that connects to the throttle body on the passenger side (RHD)

Pull the plenum and check (after you've checked the codes...)
 

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Top two guesses for vacuum leaks (without codes...) would be the plastic elbow connecting the idle control valve hoses, and/or the hose that connects to the throttle body on the passenger side (RHD)

Pull the plenum and check (after you've checked the codes...)
While you have the plenum off, check the vacuum lines from the engine to the power brake booster. Other have been several instances lately of these developing leaks; especially at the plastic Tee.
 

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Discussion Starter #12
Ok guys an update, I still intermittently get the very very rough idle when the engine is not fully warm, but I have noticed when it happens I smell fuel? No fault codes showing. The rough idle really gets violent and I can't drive off in 1st gear without jerking violently like my car's going to explode.
 

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It sounds like you're running very rich. This would account for the fuel smell and the poor throttle response, especially from an idle. The plugs are probably fouling and this is causing the poor idle, loading up on tip-in, and jerkiness. Check the plugs for signs of fuel fouling and the injectors for leakage. Be careful driving the car if the injectors are leaking as they could hydro-lock the engine.
 

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Ok guys an update, I still intermittently get the very very rough idle when the engine is not fully warm, but I have noticed when it happens I smell fuel? No fault codes showing. The rough idle really gets violent and I can't drive off in 1st gear without jerking violently like my car's going to explode.
Did you do some thing to improve the running? Last I heard you were getting a rough idle hot as well.

Are you sure you have no codes? How did you check? I would have thought running like that would trip fuel trim or misfire codes. As I said above, codes often don't light the SES.
 

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Discussion Starter #15
Thanks. No randomly it got better, so once fully warm it was running perfect, but now it's back to very very rough idle especially when the engine in not fully warm. And now I notice when the idle is rough I smell fuel. Will try take it to a place that has BMW dealer level diagnostics today.
 

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This is a long shot but I think you should remove the cabin filter box that covers the brake booster. (right side of the car for you?) Look down into the recessed area and see if it's full of crap and/or water. I've personally experienced and had a friend experience where that recess drain holes get plugged up and it fills with water high enough that the booster sucks in water. Let it get bad enough and it causes issues with stalling. Once you get water in there it's impossible in our similar climates to get it to dry out. We both replaced our boosters.
 
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