Rough Idle Diagnosis

[325_driver 422]

Having a bit of issues diagnosing a rough idle on my 2002 e46 330ci

The basic story is that when I start the car it's fine for maybe 30 seconds and then the idle is very rough, pulsating between 400 and 800, nearly feels like im about to stall when i put it into gear, no power until it jumps back over the 1000rpm mark

- only on first start

- and doesn't matter if its cold or warm in the day

- every now and then i think i can hear a mis-fire noise too from the intake during its splutter

i.e. once i've driven the car for a bit and re-start it, no issues - but start it up the next day

Has anyone had a problem like this? Or know what this might sound like

----

I've checked fault codes on a reader and it really only picks up on the mis-fires on cylinders

 

What would be the approach to diagnose whether it's like

- Coils? can coils display symptoms only on first start like this and then go away once its all warmed up?

- DISA - I thought i DISA value issue would be consistent even after car warmed up?

- ICV

- CCV

 

Any comments on this would be great before i start digging further down the rabbit hole

 

[Olaf 3321]

SCAN.  

Air leaks first starting place.

But SCAN, with someone who know's their onions.  Fastest route to a solid diagnosis.

[325_driver 422]

The scan device is only picking up mis-fire codes on 2 cylinders, no other fault codes. Thats why i'm trying to see if anyone has experienced something similar before i start dumping money into a workshop to diagnose it.

[Allanw 1071]

Has it ever had the Vanos seals done? The 3.0 is reputedly more sensitive than the 2.5, and people in colder climates have reported actual stalling from it, after a relatively short period of cold idling.

With the engine cold, at idle, the M54 using the cam timing to heat the cats faster - once warmed up, or the revs climb, it has to move the cam timing to the "normal" run position, and can struggle to do so with cold/thick oil that isn't flowing too well, then leaking past the seals when it gets to the right place.

Our old manual 525i never got that bad, but it was initially super easy to stall when cold, but not after doing the seals - cold idle was smoother, it was much harder to stall, and it was much easier to control the transition from idle to driving - there was no sudden jump in revs.

 

While it may not be your problem, I would 100% recommend doing the Vanos seals in ANY M54 that doesn't have a history of them being replaced with better parts that BMW used. Our vanos pistons literally fell out of their bores upon disassembly, because the seals were so hard, they were hardly even touching the sides.

[Olaf 3321]

6 hours ago, 325_driver said:

The scan device is only picking up mis-fire codes on 2 cylinders, no other fault codes. Thats why i'm trying to see if anyone has experienced something similar before i start dumping money into a workshop to diagnose it.

I had misfire codes and lean codes, it was PCV system.  Which scan tool are you using?  

[NZ00Z3 187]

Its likely to be a vacuum leak between the MAF and throttle body/idle control valve.  Check your short term fuel trims with your scanner to see if they are high.  Look for a crack in the rubber tube that goes to the idle control valve, its a very common problem.  Also check the tubes for the crank case ventilation system for breaks.

The vacuum leak is large enough to give you misfire codes but not large enough to push the long term fuel trims to the end of range and trigger lean codes.  The problem goes away when the engine is warm because the engine management is in closed loop mode and uses the O2 sensors to detect the lean mixture then compensate by adding more fuel.

[325_driver 422]

3 hours ago, Olaf said:

I had misfire codes and lean codes, it was PCV system.  Which scan tool are you using?  

Autel Maxisys Pro

When I grab the tool again from brothers workshop going to upload more to this post, and hopefully eventually get to the end of it so it provides some help for others in the future

thanks for replies so far

[Eagle 1662]

Sounds like a vacation leak to me too. Home made smoke machine is some of the best money I've spent.

Disa valve o-ring is another common leak area

[325_driver 422]

Bloody hell, I did this last time and couldn't spot any cracks ...

Started taking vacuum lines off again and spotted this huge crack behind in the pipe that goes to the MAF

How I didn't spot this when I last took it off is beyond me.

 

Edited December 10, 2018 by 325_driver

[325_driver 422]

Any one got one of these spare I can buy while I wait for a kit from overseas?

Edited December 10, 2018 by 325_driver

[NZ00Z3 187]

Also check the vacuum lines and blanking cap on the ports at the rear of the manifold as they crap out too, see picture.

[325_driver 422]

Thinking of doing everything to be honest - is that covered in the CCV kit usually? Or is it just a thin vacuum line - where does that one go to? Whats it for

[NZ00Z3 187]

The photo shows 3 ports, 1 x 7 mm and 2 x 3.5 mm.  Its a M54B25 manifold and all three ports are blanked off.  The blanking caps will split over time, especially the 7 mm one.  If you have a secondary air pump, it will be controlled by one of the 3.5 mm lines.

[325_driver 422]

4 minutes ago, NZ00Z3 said:

The photo shows 3 ports, 1 x 7 mm and 2 x 3.5 mm.  Its a M54B25 manifold and all three ports are blanked off.  The blanking caps will split over time, especially the 7 mm one.  If you have a secondary air pump, it will be controlled by one of the 3.5 mm lines.

Shot - hey thanks for your diagnosis with the symptoms i described - i was pretty sure it was a vacuum leak, but doubtful i was going to find anything on second look.

Maybe it just split open properly between the last time i looked

[325_driver 422]

I thought i would upload my recent addition of Temporary Fix / Hack Sins commited, since i still need to drive this car daily - and the start idle is ROUGH, cause the tear in the boot is pretty severe

Going to be waiting another week or two before the new boots arrive and other various parts from overseas

There was no easy way of doing this, and no way to avoid the mess

- After cleaning it up with some wax and grease remover - i went to town with some super RTV 

Wish me luck

Don't judge me

[KwS 2425]

Whatever works man, ain't no judging here. Just as long as it will be replaced and isn't a permanent fix lol. 

[325_driver 422]

well i started the car - it is now maybe a 5 out of 10 - instead of a 1 out of 10

Now i will patiently await the new boots - and pray that RTV doesn't magically jump into the intake manifold lol

[KwS 2425]

I will also say, your cold start idle sounds exactly like my 523i before i redid the vanos on it. issue was gone after that

[Gabe79 410]

I had nearly this exact same problem description. It was a vacuum leak. There was a good crack on my valve cover. 

Highly recommend you find someone with a smoke machine. I spent months with the problem, then a mate found the crack (it was a large crack...) in 5 minutes.

[325_driver 422]

I was awaiting your response Gabe -  I knew all that RTV would get your attention

[325_driver 422]

Can the vanos seals be leaking / causing power loss without any engine codes being triggers? What codes would you expect being fired if vanos is leaking?

Debating getting the rebuild kit in the new year once i've done all the vacuum and CCV kit stuff.

[KwS 2425]

My car had no CEL, no codes. Just ran like a bag of dicks when cold, with the idle surging. Was also down on power when warm, but wasnt too bad.