idling badly from cold for 30sec

[dizz]

my 1990 318i (110.000 miles) is iding badly from cold, but by the end of the road (30-60seconds) will idle fine, it does not miss fire at any time and has a new set of spark plugs, there is a slight blow from the exhaust manifold, any ideas?

thanks

[Brianmoooore]

What do you mean by "idling badly" if it's not a missfire?

[Bob_S]

I think it is possibly to do with the choke? probably not enough fuel getting into the engine for the first 30 secs or so then once it's started circulating it's ok, maybe fuel pump? I'm guessing again sorry

[jonmsm]

hi there,

I used to have a e28 520 and it used to do the same. It came down to being a problem with exhaust valves being burnt, but mine was made much worse by the fact one cylinder was loosing all pressue and not fireing. However, this bad idleing is not really that uncomon really with an older car. It can also be to do with the idle which I believe is automatic on the 318i (assuming its not on carbs) . not sure how to sort that thou.

[dizz]

What do you mean by "idling badly" if it's not a missfire?

ok, i see what you mean, what i should have said is that when you first pull away its smooth and fireing on all cylinders, i just have to keep it going geting off the drive and until im pointing in the right direction.

[Brianmoooore]

Still not sure what you mean, but if it's sparks, sheck the distributor cap and rotor.
If it's fuel, check the blue temperature sensor, screwed into the side of the engine, under the inlet manifold, about half way back.

[dizz]

I think i will check the blue temperature sensor because if it thinks the engine is warm at a cold start it would be under fueling, then once it starts to warm up the amount of fuel would be correct which is why it then idles ok. does this make sense? or am i losing the plot?

[Brianmoooore]

That makes perfect sense.

[jonmsm]

sounds like a good place to start as, like you say, when the engine is cold it uses more fuel (essentially what the choke does). In more modern cars they have a seperate injector in the intake manifold just for that, which adds a small amount of extra fuel on cold starting to allow the engine to idle smoothly and warm up quicker. So if your engine thinks its already warm it wont bother with adding the extra volume of fuel so essentially its a bit like starting it up with no choke which causes problems in keeping the engine going on idle just as you describe.

Give the sender a check and if that brings no joy then it could be your idle control valve but this is more likely to cause a lumpy idle cold or warm.

Let us know how it goes and if that doesn't sort it we can try and figure out what else could be wrong and fix it.

[Brianmoooore]

Only early cars had a seperate cold start injector. Most E30s increase the duty cycle of the normal injectors to provide the extra fuel for cold running.
Problems with ICV don't really give a lumpy idle, just a varying idle speed, which might be a bit rough if it's too low.

[dizz]

Is there an easy way to check the sender, or is a case of fitting a new one, if so does anyone know how much one would be?