Bmw 335i Rough Idle at cold start

[Olvmini]

Got a 2007 bmw 335i which Rev hunts when on cold start but runs fine and starts fine after the initial cold start. Recently it’s been throwing a half CEL on cold start when idle rough. Have change the iat sensor as was getting other code which have no longer come back and rest the adaptations using MHD. The car is on the MHD stock tune as I originally thought that it could of been the map that the previous owner has put on there. Always use Shell V Power. Cars done 82,000 miles. The codes I’m getting on cold start are 29DC, 29F2 and 2F6C however I don’t think that one is related!

[TheGreatDane]

Does it start first time or does it take a few cranks before it gets going?

[Olvmini]

It starts first time and for a couple seconds it’s fine then sound roughy and throws the injection cut cold as well as the hpfp

[TheGreatDane]

Sounds like its your hpfp.

[Olvmini]

Is there anyway of testing this? I’ve also heard that sometimes the lpfp sensor if gone bad can trigger the hpfp to throw a code?

[MattOz]

Had something similar when I had mine. Turned out to be a cracked rocker cover, leading to plugs getting oil misting on them and not liking the cold start. Was fixed under warranty. Might be worth a look.

[Thepaperboy]

My son had very similar problem to yours in his 140i and always used V power. I drove it one day and it needed fuel and the nearest station was a BP and I filled it up with Ultimate and the next morning my son said the cold rough idle had gone changed back to V power and the rough idle returned. We have always used V power and still do in another cars and have had a never issue except in the 140i,so it maybe worth a try.

[Olvmini]

Other than visually inspecting the valve cover is there any other way of checking?

When it’s nearly empty I’ll try switch to any other fuel and let you know!

Your help is very appreciated!

[survivalist]

TheGreatDane said:

Sounds like its your hpfp.

I’d second this. Mine did it for months before throwing a fault code. Then another few weeks before it gave up completely.

You can try and do a few full throttle runs, if it goes back to a really rough idle that’s a telltale sign.

[Thebaggers]

Has it been through any standing water recently?

[Olvmini]

I have done a couple full throttle pulls to the top of 4th and haven’t had any problems. After about 30 seconds of starting from a cold start and it’s fine. Any other time it’s started during the day it’s completely fine!

[RUSSELLM]

Could it be oxygen (O2) sensor related ? I presume it’s supposed to be running in Open Loop for the first few seconds.

Edited by RUSSELLM on Thursday 7th January 05:16

[Fiedka]

On an N53 that is a sign of injectors failing.
Not sure why would it be HPFP?

[DaveE87]

Thepaperboy said:

My son had very similar problem to yours in his 140i and always used V power. I drove it one day and it needed fuel and the nearest station was a BP and I filled it up with Ultimate and the next morning my son said the cold rough idle had gone changed back to V power and the rough idle returned. We have always used V power and still do in another cars and have had a never issue except in the 140i,so it maybe worth a try.

In my experience it's usually older cars that prefer BP Ultimate petrol as they don't mix in ethanol - my old M52 ran perfect on BP Ultimate but was never as smooth with Tesco Momentum or Vpower (I think due to the ethanol). I now have an N52 which is obviously a more modern engine and it runs fine with all three, so I tend to stick to Momentum as it's cheapest.

[Olvmini]

Just a little update. Thought I’d put a different fuel in so I put tescos momentum in and on a couple of pulls it’s started misfiring (well sounded like it) but no engine light! Stoped the car turned it off and back on again and then it was fine!

[RocknRollOutlaw]

Sounds like an injector.

[Olvmini]

Yesterday I decided to pull the covers off and saw that the injectors have already been replaced and look new. Thought I’d check the fuel pipes and everyone was ‘loose’. Tighten all the pipes and left it over night and start this morning and not a problem! Holds idle, no miss fire, no codes. However it’s is a bit warmer this morning compared to how it has been!