1993 Mercury Topaz exhaust manifold turn a glowing red and

Engine Mechanical problem
1993 Mercury Topaz 4 cyl Front Wheel Drive Manual
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I have replaced egr, tps, map sensor, throttle body , cat converter, all vaccum hoses, mass air flow , idle air control valve and fuel pump, upper intake manifold gaskets, and ecm. however it still has a high idle and the exhaust is glowing cherry red can please advise thanks in advance Chris