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Old Wed, Jun-03-2009, 06:46:16 PM   #76
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I found this SIB for E9X M3s and E6X M5/M6s regarding rough idle in relation to "mandated emissions requirements". Draw your own conclusions and/or theories.

"SI B 12 28 08
Engine Electrical Systems
December 2008
Technical Service

S65 / S85 Rough Running During the Catalyst Heating Phase

E90, E92, E93 M3 with the S65 engine
E60 M5, E63, E64 M6 with the S85 engine


These engines may exhibit rough running characteristics during a warm-up period after they are first started.

Once the engine is at operating temperature, the running quality is normal.


To meet mandated emission requirements, the engine must operate on a leaner air/fuel mixture during catalyst heating.

This strategy is necessary in order to bring the catalysts up to operating temperature quickly. This catalyst heating phase lasts for approximately 30-40 seconds following a cold engine start.

If the rough running is only present when the engine is cold (warm-up phase) and no faults have been stored in the DME control unit, the customer should be informed about the particular design of M-type engines.

This characteristic of "lean operation in the catalytic converter heating phase" is described in the Owner's Manual under the section "Driving hints", and should be used to answer any questions in the event of a customer

If error codes have been stored in the DME control unit, they must be worked through according to the test module/test plan."

Let me know if this sheds any light on the subject in relation to E46 M3s.
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