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Discussion Starter #1 (Edited)
You ever read the threads about cold weather startup misfires that don't get solved and they
just end and there is no definite solution to the problem? I have read just about all of them.

This thread is an update to a thread I started last spring found here.

So my cold start rough running during the SAP (Secondary Air Pump Operation) time period
was still present even during the summer months as has been the case for some time,
it is more intermittent during the warmer months and almost imperceptible, but I
know when it occurs. When ECU goes into closed loop operation, the idle is fine,
this only occurs during the open loop operation while the secondary air system is in

It gets worse during really cold periods and really rears its ugliness, last winter my car
indicated some misfire codes during a cold snap below zero warming up the car, misfires on
cylinder 4 and cylinder 1. Changed coils around, new coil boots etc. no change.
This does not happen if I just drive the car immediately after starting up.
Only 1 time did I get any codes for Secondary Air System too lean, that was a 1st
last winter.

Last fall I did all the tests of my SAP system and it works just fine except that my
vacuum at the secondary air check valve was only reading 8/hg of vacuum,
all my vacuum lines are new all the way back to the electric valve and to the
1 way vacuum valve and to the intake manifold, also the plastic vacuum tube has
no cracks in it.

Picture of vacuum at the air secondary air check valve during cold startup SAP operation.

IMG_0262.jpg Should be 15/hg vacuum.

Vacuum tested at the port on my intake manifold where the SAP 1 way valve attaches indicated 20/hg of vacuum.
Gotta be that the 1 way valve is clogged or the electric valve is not functioning correctly.

Replaced the 1 way valve, (it was clogged up compared to the new one) and replaced the electric valve on the back
of the intake manifold for good measure. Now I know how to get that bugger out of that ridiculous spot that BMW placed it.

All should be good now right..? Nope, car still doing the same thing. Fires up at first turn of the key, idle goes up to 1100 RPM,
about 5-10 seconds later it drops down to about 850 RPM, it should stay at about
950-1000 RPM during the SAP operation period, (70 seconds on my car).

Fast forward to last Thursday morning, 17 Degrees cold morning start up. Car fires up
at first turn of the key and then settles to 850 RPM during SAP operation, really bad misfires
but as usual no codes and cleared up after driving away. Drove it to work and it sat for about 9 hours.

Walked up to the car after work and decided before starting it i'm gonna unplug the MAF and see what happens,
it's 26 degrees at this point, car fires up as it always does first turn of the key and BAM, idles just as it should and the idle
hangs around 1000 RPM, no dropping to 850 RPM. I quickly shut down the car and reconnected the MAF and started it back up,
engine continued to run through the SAP period and the idle stayed where it should with no rough running.

It has been 4 days and the cold startup misses have not returned. I even let the car sit
for 2 days and it has started up and no misses have occurred.

I have had my MAF disconnected while doing work on the car many times and I always make sure it is connected correctly,
must be time to clean the MAF connector (wire loom side) as the MAF is less than a year old, (Siemens VDO MAF)

By all appearances, the MAF connector appears just fine, no corrosion or misadjusted
connectors as I have examined it in the past, but something is amiss with it.

For now I am not gonna touch the MAF connector until the problem starts up again.

I conclude for now that it is my MAF connector, (not the MAF) that has been causing my
cold start rough idle issues during the SAP operation period.

In all that I have read on this subject, Cold Startup Rough Running E39, I have not run across this as being the source of the problem, apparently it is the problem in my case.

I can't believe it was this all along. Hope this helps.
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