mixture settings

[E36-italia]

With my '94 car... I suspect that the mixture is a bit off.

idle isn't perfect constant... and on the overrun i hear a slight rumble in the exhaust (which should be a good sign, engines need to be rich on overrun)

The reason i suspect it's not perfect, a while a go did some hard driving
(well I was, but my dad behind me not...in his V70 R AWD)
and my dad told me that there was absolutely no smoke...zero... but under accel. he could smell it.

Is the ECU a self learning unit, or do i need to plug in a laptop and change the mapping myself?
or more simply, does the airflow sensor have a possibilty to richen her up a bit (by adjusting the flap angle a bit)

[DesktopDave]

Vac leaks in the hoses, or the idle control valve.  The M42 is infamous for both.

The ECU (or DME according to Bosch) does self-learn and adapt.  That's why the idle surges.  You can't change the mapping yourself unless you're handy with DIS or have full access to a GT1 (BMW dealership computer).

If the hoses are 100% and the ICV is perfect, you can also tweak the spring pressure on the AFM door.  There is also a bypass screw on the older BMW AFMs to tweak CO emissions at idle, was under a little plastic plug.  I'm not sure if it's still there on the M42 AFMs.

[E36-italia]

how the ICV is, i have no idea.. the car came with no service history... could be 16years old.

There are 2 vacuum hoses that aren't very good anymore.
The one from the valvecover to the inlet manifold... and there is one small diameter from the upperpart of the inlet manifold going down to something unknown very low into the engine compartment... and that small one is quite gone now.


I have access to an engine dyno (not a rolling road) so ECU readouts shouln't be problem...but to remove the engine for sorting out the idle (cold start on 3cil..hot on 4) and it's lean acceleration feeling is a bit of work...for a non racing car.

[colin86325]

If the hoses are 100% and the ICV is perfect, you can also tweak the spring pressure on the AFM door.  There is also a bypass screw on the older BMW AFMs to tweak CO emissions at idle, was under a little plastic plug.  I'm not sure if it's still there on the M42 AFMs.

I would recommend against tampering with the spring tension of the AFM.  It can prove to be a diagnostic nightmare down the road.  The M42 AFM does not have the CO adjustment that the earlier E30s have.