Ford Escort 1991 "Check engine" light

[Dmitry Samsonov]

I own a Ford Escort 1991 with 1.9 l fuel injected engine. It runs fine,
except maybe some loss of power especially noticeable in mountains, and
somewhat rough idle.
But if I drive on the highway at about 60-70 mph "check engine" light comes on.
It stays on almost all the time I am on the highway. The car has high (117,000) 
mileage.

I checked the EEC error codes and got 41 (No HEGO switching detected) and
63 (TP (throttle position) sensor below test minimum). After replacement of 
the oxygen sensor the first error is gone but not the second. Spark plugs
and all the filters have been changed recently too.

What might have caused this error? Is it nesessary to readjust the throttle
position or is it an injector problem?

Thanks.
Dmitry