Rough cold start issue.

[ben g]

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]

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]

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]

Isn't that the idle valve that needs cleaning?

 

[ben g]

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]

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]

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]

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

 

[hopz121]

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]

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

 

[ben g]

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]

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]

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]

Sounds promising.

 

[Bkbkbk84]

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

Thanks

 

[enuff_zed]

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

Thanks

The ICV is a little fiddly to access, but not too bad if you take it steady and make sure all the hoses go back on tightly.
I recently picked up an E85 with the M54 engine that had no idle issues at all. I removed the ICV as a matter of course, simply to remove all the crud that builds up over the years. It did still move but reluctantly. 10 minutes with some carb cleaner and a good twist about to get it moving and it's much better.
I'd suggest that you should try cleaning it up anyway if it's never been done before.