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Message: <blockquote data-quote="aidilj" data-source="post: 666727" data-attributes="member: 20536">Yup the N42 (ME9 DME) will rev the engine up and down during idle if there is a leak after the MAF. During cold start the engine vibration would be worse because it depends solely on the input from MAF and not O2 sensor, and air that gets into the engine is much more than metered by MAF so the engine is running lean.After the engine (O2 sensor) is warmed up, it will start to use O2 sensor reading and will be able to trim the fuel accordingly. A conflict between metered air and air fuel ratio will cause the DME to rev the engine up and down. Cheers</blockquote>