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Clean them and reinstall...you can swap if you want, or just see if the code goes away. If it comes back, try swapping and see if the code follows the solenoid to the intake side. Then you know you need to replace that solenoid.
If you are still getting a code on the exhaust side after cleaning and swapping, then its most likely another issue (probably bearing ledges, though not sure they were an issue on the M3?)
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