Toyota Repair: 1990 Camry CEL, blown head gasket, air fuel mixture

Question
It is showing both codes 25 and 26 with no other obvious problems.

Any likely suspects to start with first?

Answer
The 25/26 codes are air fuel mixture related, the system is changing from rich to leean instead of staying at the normal ratio, this is normally caused by an engine misfire or a leak on the intake system, check for any disconnected or broken hoses, check the spark plugs and wires, cap/rotor etc. It may be necessary to have the engine checked for cylinder compression loss or a possible blown head gasket.