1993 4x4 Legacy wagon, 5sp, non-turbo 210,000 miles. 

 

Every day when I drive to work, the check engine light comes on in almost exactly the same place, just before the car reaches normal operating temperature. 

 

Sometimes the light goes off after a few minutes, other time it stays on untl I shut the car off when I get to work.

 

The car seems to run just fine even when the check engine light comes on.

 

I can get a trouble code number 42 out of the memory, when the light is on.

 

I have changed the temperature sensor, the Idle Control Valve and the Idle Contro Switch, none of that has made any difference.

 

Anyone out there have any ideas what to look at next?

did you check the wiring going to those parts?

 

Old wiring can get brittle, and the insulation can crack...

 

also check the insides of the connectors for corrosion and/or dark/burned looking areas = bad connections

Yes, all of the wiring and the connections looks good.