Rough idle when cold

[bob53]

Hi
Got a problem after starting,car idles really bad for about 10 minutes until warm then is OK.
I have checked for air leaks around intake and maf, cleaned ICV ,has had new air filter dizzy and leads fitted by previous owner 2 months ago.

What else can I check? does this engine benefit from an ECU reset(battery of for an hour)?
E30 316i m40 1994 touring

Any help would be appreciated

Bob

[beardymat]

if it only does it after its been stood a while it could be that youve got water seeping into one cylinder,the water stops fuel from igniting properly and causes the missfire but it gets expelled slowly and then everything returns to normal,one way to tell if this is the case is to remove the plugs and see if one is significantly cleaner,this is because of the steam cleaning effect,also you will be loosing coolant.if not im talking out of my butt.

[bob53]

Hi Beardymat
Just been out and pulled the plugs and they are just fine have also got the MAF of at the mo to give that a clean,doesn't look to bad either.
Have noticed the fuel pump seems a bit noisy.
My next job is the fuel filter, but I would expect the engine to be rough all the time if there was a fault there.
I will disconnect battery to see if that will reset the ecu just in case there is a stored fault!!!

I will keep trying and let you know the results.

Bob

[bob53]

Just put everthing back ,started it up and seemed as though it was misfiring.
Had to keep my foot down until it warmed up but it still spluttered.
Can someone tell me where the fuel filter is, the online ETK shows one at the tank and one in the engine bay( I think this one is the return filter)
I might try and bypass the tank filter to eliminate that??

Bob

[Jos]

If it is only doing it until it warms up then it has to be heat related surely? Normally if the temp sender is faulty the engine runs rich when warm, yours is the other way round, rough cold idle then ok when warm. Still worth checking them though. The other thought is the fuel might not be atomizing correctly when the engine is cold, but the heat from the block once it warms up is helping that along and allowing the engine to run properly.

From your description it sounds temperature related more than anything else. As you say fuel filter would be rough all the time. Have a search about on the forum for thermostat or temperature sender.

[Martinaston]

You didn't mention the spark plugs, might be worth cleaning them if there not new they could be getting fouled with the rich mixture at warmup.

[bob53]

Look up 4 posts I did check plugs and they where like new.
I havn't found out yet why the fuel pump keeps going before I start the engine,maybe that is faulty I will try and have a look in the morning

Bob

[Martinaston]

The fuel pump activates to prime the fuel system up to pressure before you turn the starter, thats normal.

Have you cleaned the inside of the throttle body?
If it has a build up of gunk on the inside of the venturi it will restrict the flow of air at idle and cause it to run rich.

The throttle should also make a click as you move it about 0.5mm from the closed position. If it is not clicking then all the other setting's will be incorrect and cause other problems.

[bob53]

HI Martinaston
I havn't done the throttle body yet but will look at it today.
I got the Haynes manual late last night, and according to that the fuel pump comes on when key is in pos 2 and goes off until engine started and running, maybe I read it wrong so Iwill go through the manal again.
I still need to clarify which is the main fuel filter.

Bob

[g57yle]

it looks like the ecu is seeing a warm engine and supplys inadequate fuel until it warms up.