Rough idle

Andy Comerford

Andy Comerford

Dedicated Member
British Zeds
Joined
Oct 29, 2015
Points
29
Location
Birmingham
Model of Z
Z3
Hi guys!

I was changing over some pads and disks the weekend and when I was driving home from my friends house i noticed my 1.9 Z3 had a rough idle (sounds like a lumpy v8!). It doesn't effect the car moving or driving at speed only when stationary. It even quickly revs itself to about 2k occasionally when stationary too.

I assume this might be an air leak somewhere but before i start digging around for something thought id ask the guru's what they think or any experience with this!?
 
You definitely need a diagnoze check and a visual check for the air hoses. Could be a sensor too.
 
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So I found that after a fiddle with these line attached to the rear of this component the little whine noise that I was hearing stopped and the idle seemed to level out so I'm guessing there's a little split or are just a little worn as they were quite soft. Although, what is this circular part here? As the small triangle on the top seems to be dispelling air and I'm not sure if this is right as I'm not even sure what it is!

Any thoughts on this?
 
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The hose coming in is recycling the vapers in the engine. If it's cracked it will have almost the same effect as taking out the dip stick. More than probably it's old, hardened and cracked. Keep searching with a flash light and a small mirror ( like dentist use when checking our teeth).
 
The hose at the front of the picture with the sliver clip round is fine, it is the hose at the top of the picture running out back in to the car that was soft. So should there not be air coming out of the triangle on that round plastic part? If not does anyone know the name of it so I can replace it?
 
My suggestion is to change those two hoses, same as the big one who splits in four to each injector and check also the large one between the maf and inlet. All rubber components in the engine bay are overdue to age and heat. They aren't expensive but can create a lot of trouble.
 
You have to turn on the real OEM diagram and to chose the parts according to your VIN.
 
I see in the pic a piece of textile under the cap with the triangle? It shouldn't be there.
 
That is your crank case valve. The hose that runs from it goes to the top of your rocker cover. Pull that end off and look in it. If it looks like this...
IMG_20160219_152340962
...then it's blocked with oily deposits and needs changing- the hose that is. The vent is probably ok as the oily deposits don't make it that far it seems. If the CCV itself is damaged you would be able to see it I would have thought?? To take it off is just two allen bolts and the hose pulls off.

My guess is that this isn't your issue though...
 
Thanks @Wookee! I'll have a look on the inside of that hose later today. Should the CCV be expelling air from the little triangle on the top constantly? Nothing looks broken on it and it pretty much looks like it should but just seems odd a part that releases air. I can cover it up with my thumb and actually makes the bay quieter not being able to here to air coming out!
 
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Hi, that's a PCV ( banjo Valve) it shouldn't vent to atmosphere, so its blocked or bust.
I would start here, https://zroadster.org/articles/m44b19-fuel-injector-replacement.76/
have a look at all of the rubber hoses from the injectors, all the way back to the PCV, plus the flexi boots from the Air filter to the throttle body too. The job might look daunting but it took me a couple of hours and made heck of a difference. The boots from BMW are only about £12.00 to £14.00 each I think. Don't know about the smaller tubes cause I use generic stuff & cut to length.
The PCV can be washed out with gunk & boiling water, then you can do a suck/blow test.
Have fun
 
Just thought I'd add some info and photos about PCV/CCV's This wikipedia item explains what they do

I have changed mine, along with the hose, and have taken the old one apart.

IMG_20160308_151902147
IMG_20160308_151914732
IMG_20160308_152043729

I have had a close look at it and it is designed to let a little air escape. There is a gap under the triangle that leads to the small hole pictured.

IMG_20160308_151935309
IMG_20160308_151952305

My engine is an M43 so is slightly different and this is how mine is set out. Pull the end indicated by the blue arrow off and look in it, if it looks like my post above then change the hose. Personally I wouldn't bother changing the CCV itself, just the hose. Unfortunately, BMW sell them as a pair, attached to a coolant hose with some rubber tubing and glue. If you don't fancy draining the coolant then just separate the two pipes and cable tie the new CCV one to the old coolant hose.

IMG_20160308_151439054
 
Having said all that:), I doubt this is the cause of your problem. I'd be looking at your air intake hoses(s) and your idle control valve first. Replace the former if holed or if it's the ICV then it will just need a clean.
 
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