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The usual cause of the symptoms you describe on this particular engine is a failed plenum gasket. If you pull the plenum off, you will probably find the gasket sucked in creating a vacuum leak near #5 cylinder. <smile> being such a common failure, all chrysler dealers stock 'em, i think they are less than 5 bucks and pretty easy to change. If you have a smoke generator available, it usually makes them show right up before disassembly.
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