Rough cold start issue.

ben g · Post by **ben g** » Sat Nov 28, 2015 6:18 pm

Can't seem to get to the bottom of this. It doesn't always do it, but when it does, it runs like a pig for a few seconds until I pull away and start driving as normal.

I replaced all the ignition coils with brand new Bosch ones and also replaced the CPS sensor with a new BMW one.

Anything else that could cause this? It pops a few times, revs drop quite low as if it's about to stall, so I put the clutch back down and then it's ok to drive away.

Spark plugs I assume were changed during the inspection 2, although I will double check this with the indy I used just to make sure.

If possible, i'll get a video of it happening. That might help diagnosis.

Car runs perfectly fine otherwise and theres plenty of power there, so i'm not too worried. It's just a bit embarrassing and annoying.

mr wilks · Post by **mr wilks** » Sat Nov 28, 2015 6:25 pm

Is it always when car has stood so fully cold or can it happen if restarted within a short time of it being fully warmed ?

ben g · Post by **ben g** » Sat Nov 28, 2015 6:32 pm

Only when it's been stood overnight or after work so at least 8 or so hours. If I come home, leave it for an hour or so then go out again it's fine.

pvr · Post by **pvr** » Sat Nov 28, 2015 6:35 pm

Isn't that the idle valve that needs cleaning?

ben g · Post by **ben g** » Sat Nov 28, 2015 6:50 pm

Just had a quick search on the ICV and it could well be that I guess. I've never had it off to clean it, though I did replace the DISA flap.and that 3 legged rubber hose so should be easy enough to remove.

I would've thought the ICV would make it run rough constantly, rather than just on cold starts?

Steve84N · Post by **Steve84N** » Wed Dec 02, 2015 1:46 pm

Different airflow circuit for cold start than normal idling. You'll notice your idle speed is higher when cold but lower at all other times including restart when still warm.

ben g · Post by **ben g** » Wed Dec 02, 2015 5:15 pm

Ah yes indeed it does! Cheers for that.

Laat night I manage to pull away from my house with no dramas. Got to the top of the road after about 20 seconds and it started idling very erratic, to the point it felt like it was going to stall.

Had to clutch down, brake on and wait a few seconds for it to clear. After that it was fine.

Does that sound like a definite Icv fault?

Steve84N · Post by **Steve84N** » Thu Dec 03, 2015 9:28 am

If your battery is in good health then it does sound like the IACV as the problem is focused on that scenario.

hopz121 · Post by **hopz121** » Thu Dec 03, 2015 12:53 pm

I would say ICV I plan on cleaning mine over the next few weeks, think there is a good how to on YouTube on an E46.

How easy was the CPS to fit and how much was the sensor from BMW out of interest?

aquazi · Post by **aquazi** » Thu Dec 03, 2015 2:42 pm

Another possibility is a dirty MAF especially if you have an oiled air filter.

ben g · Post by **ben g** » Thu Dec 03, 2015 3:00 pm

hopz121 wrote:I would say ICV I plan on cleaning mine over the next few weeks, think there is a good how to on YouTube on an E46.

How easy was the CPS to fit and how much was the sensor from BMW out of interest?

CPS was quite easy to fit, just a bit fiddly as you need to route it behind the oil filter housing and it connects just in front of the ICV from what I remember. Easiest way is to remove the airbox so you can get some decent access.

I also remember it being a bit messy when removing the solenoid. Had to clean up some oil leakage. Probably took about 30 mins, so easy enough to do on your driveway.

ben g · Post by **ben g** » Thu Dec 03, 2015 3:02 pm

aquazi wrote:Another possibility is a dirty MAF especially if you have an oiled air filter.

Hi aquazi. Originally that's what I thought it was, as I had a small flat spot at 1500rpm, but I have a standard airbox on now and no problems anymore, apart from this erratic idle, only when cold. I'll clean the ICV and if that doesn't fix it, I'll try and clean the MAF

ben g · Post by **ben g** » Mon Dec 07, 2015 1:42 am

Thanks for the heads up on the ICV. I removed it today and the valve inside was stuck due to the amount of soot inside it! Sprayed some brake cleaner through it and the valve now moves freely. Re-fitted but haven't tried a cold start yet to check whether the issue has been sorted.

But, it must have done some good to have a freely moving ICV!

Steve84N · Post by **Steve84N** » Mon Dec 07, 2015 2:43 pm

Sounds promising.

Bkbkbk84 · Post by **Bkbkbk84** » Wed Sep 08, 2021 9:26 am

Did this cleaning ever resolve the issue? I’m trying to trace down a slight rough cold/ semi cold rough idle currently..

Thanks

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