Have some one smoke the engine to find vacuum leaks. To smoke an engine means to seal up the air intake, pcv system, etc then inject smoke into the vacuum system with a smoke machine and then look for smoke coming out where it shouldn't. Also, what kind of plugs did you use? Any thing other than NON-RESISTOR COPPER CORE PLUGS can cause the problem you have.
Paul

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84 500 SEL (307,xxx miles)