Revs briefly hunting on start up

B

BuzzardBiker

Member
South Beds
So for the first time I noticed today that the car started and the revs/idle was hunting / erratic for a few seconds before settling to a steady 750rpm.
3.0si Auto.
I’ve seen a couple of YouTube videos including this symptom and wanted to know if I can cure this by either using a diagnostic device, like the one in this link - https://www.ebay.co.uk/itm/154021453500
Or if a battery disconnect and reconnect will resolve the gremlin.
Car itself runs beautifully smooth.

Thanks
 
Warm or cold start?
Ive had 3 N52 engines and all of them had a slightly lumpy idle when starting with a warm engine..
For 5seconds after initial rev drop.
 
Warm-ish.
I took the car out earlier today and then again about 2 hours later so I guess the engine was still pretty warm.
 
Doubt it’s anything that could be reset with BMW scanner. Sounds more like either dirty injectors, dodgy coil pack or possible vacuum leak in the pipes.
I have the same issue. Swapped a couple of the coil packs around and the issue seemed to die down. Makes me wonder if I should just renew them all.
 
Project Spa had a similar issue but much worse. This turned out to be due to low oil pressure caused by the basket in the oil filter cap being loose.
 
enuff_zed said:
Project Spa had a similar issue but much worse. This turned out to be due to low oil pressure caused by the basket in the oil filter cap being loose.
Click to expand...

I have thought about this as the car was serviced by a non BMW specialist/dealer.
They replaced the rocker gaskets and did the oil change. 6.5 litres of 5w30 (I will change to 5w40 in due course). So I did wonder if they put the cage in at all. I would have thought they would do seeing it would have been attached to the old filter and not the new one. I haven’t got the oil cap tool to remove and check. Just a band one which slips. Might try and get some elephant tape on it for more grip.

I will check the revs next time I start the car from cold. Just to get a better idea.
 
chanlon1 said:
Doubt it’s anything that could be reset with BMW scanner. Sounds more like either dirty injectors, dodgy coil pack or possible vacuum leak in the pipes.
I have the same issue. Swapped a couple of the coil packs around and the issue seemed to die down. Makes me wonder if I should just renew them all.
Click to expand...

The BMW Doctor on YouTube has a video having the same idle issue and he disconnected the battery and then got jump leads and bridged the terminals. He said it takes a few minutes but the car resets itself.

I don’t want to copy without knowing if I would cause any problems following that process.
 
Ok, so I just started the car up from cold and get the hunting revs before it settled down.
I checked the oil filter and can see the cage is still there so that’s good.
I did notice a little whining noise coming from the oil filter housing (cooler part) and wondered if that is normal on a cold start. It does disappear once the car is warmed up.
After reading about this noise it could well be a cheap oil filter causing the noise.
So I am going to replace it with either a genuine BMW one or a Mann version.

Any further thoughts are welcome.
 
BuzzardBiker said:
Ok, so I just started the car up from cold and get the hunting revs before it settled down.
I checked the oil filter and can see the cage is still there so that’s good.
I did notice a little whining noise coming from the oil filter housing (cooler part) and wondered if that is normal on a cold start. It does disappear once the car is warmed up.
After reading about this noise it could well be a cheap oil filter causing the noise.
So I am going to replace it with either a genuine BMW one or a Mann version.

Any further thoughts are welcome.
Click to expand...
When you change the filter, check how the cage sits in the cap. It seems it only has to be a little bit loose to cause an issue.
 
chanlon1 said:
what's this oil cage you are referring to? Never heard it before.
Click to expand...

It’s (I think) the cylindrical cage assembly the filter sits on in the filter housing.
 
Had a check around the forum and found this post that has a good photo of it. I personally havent changed the oil in my ownership, BMW did it a couple of years ago for me. Makes me think I may pop open mine to see if its in there...I would like to assume it is, if BM did the change .....

https://z4-forum.com/forum/viewtopic.php?p=1682425
 
I’m going to change the oil soon. Although 5w30 was used in the service last month, I’ve know idea what quality of oil the dealer used so for peace of mind I can invest in some 5w40 and a new quality oil filter.

However, I don’t think this will cure the idle issue on start up. Not that it is a problem as such but if there is a way to resolve it then I will look to do that.
 
chanlon1 said:
Had a check around the forum and found this post that has a good photo of it. I personally havent changed the oil in my ownership, BMW did it a couple of years ago for me. Makes me think I may pop open mine to see if its in there...I would like to assume it is, if BM did the change .....

https://z4-forum.com/forum/viewtopic.php?p=1682425
Click to expand...

This recent video has the cage in it at 5 minutes. Good to know about it in general.

[youtube]ggnkh651WBA[/youtube]
 
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