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Old 03-03-2013, 02:22 AM   #5
Registered User
Join Date: Jul 2012
Location: Portland, OR
Posts: 3,366
My Ride: 2003 330CI Silver
Issues like this always remind me of something electrical or related to electronics. Don't get a new ecu, that's just plain retarded. With my experience and background in electronics, computer software, programming, and anything electrical, you can sometimes have a partially functioning piece of electronics but my rule of thumb is it either works, or it doesn't. This isn't really a good rule to go by but if it pertains to the ECU, I think it does. Perhaps you may try dabbling in the art of ecu upgrading and see if that helps that and updating your tranny software. The sporadic fault seems interesting. I've also had the error 91 happen to me before too as well. It ended up being a voltage power issue, the fluctation and unstable volts due to perhaps (havent seen the error anymore but still having seldom voltage issues which I blame power steering fluid leaking on to my alternator) my alternator issue. I don't think its failing because I noticed residue from power steering atf fluid on it, and whenever I clean it, it works fine. all in a nutshell, power or voltage wild swings can easily be a cause of a lot of errors, throwing error codes and making you think its one thing when its not.
Portland Metro: ECU updates, Euro tune, euro corner delete, air bag light, DSC light, cluster and any led color change, soldering work, transponders for keys, and all custom work related to computer or electronics.DIY AK90 A walk through on coding your mcu and transponders EWS3 How to make your own key (ak90 review)
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