Yes, check the KE system one last time (though you have done most of the tests already), and if it is not the KE system the only thing I can think of now is vaccum. Perhaps a clog in the exhaust system.

You should confirm that the sensor signals are indeed reaching the ECU (i.e. if the harness is o.k.) Specially the coolant temp sensor cables.

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Saumil S. Patel