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Old 08-11-2003, 02:52 PM
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Thomaspin Thomaspin is offline
Join Date: Jun 2001
Location: CA
Posts: 531
Have you checked the intake manifold seals? The M116 engine I illustrate this on is a 380, similar to your 420. Idle was very rough and intake leaks were detected by pumping inert white gas into the engine at the local independent mechanic's shop. Lots of hours to do, little $, similar symptoms to yours.
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