We have cleaned the throttle body and have done the following: crank sensor, stator, idle air control motor, oxygen sensor, EGR solenoid (we cleaned the EGR valve), ignition wires, plugs, distributor cap and rotor and fuel filter. In addition I've replaced the muffler, heater core, blower, resistor, oil pan gasket, rear main seal, PVC assembly, vacuum harness and battery. Do you think an EGR valve can appear to work but not actually be working... Needing to be replaced?