Have 93 60 Spec. that won't change from open to closed loop causing excess fuel use.

Easiest way to cause change is to run air conditioner. Then, fuel use is proper but upper components of engine change from abnormally cool to very hot. For example, air cleaner is very hot to the touch. It is as though exhaust gas was mixing with the intake air. Could their be a misconnection of EGR or other vacuum lines? Car (when hot and running in closed loop) easily passed emission tests. Recent engine diagnostic tests by well qualified shop showed no engine related codes.

Very anxious to get ideas & help.

 

bump ...

 

thermostat stuck open will allow it to run too cool. will rarely go into closed loop unless more engine heat is added like turning on the a/c.