1998 S70 T5 and I've replaced the MAF sensor with a part from another
car that it is known good.

Yet, I still get a check engine light after driving for a while so
definetly not the sensor.

Is that harness often faulty?

Is it easy to replace?

Anything else that's a possibility?

It may be heat related the way it's acting and I saw on some earlier
cars there is a thermostat that controls the air filter temp?.....but
see nothing like that on my 1998.

Appreciate any thoughts.  Thanks.