Toyota Repair: 92 Corolla LE 1.6 4AFE (FI) AT Calif Emissions 143K Miles, mass air flow meter, air flow meter

Question
2 Days ago started running very rough at idle, thru the acceleration range & at speed w/ some smoother spots.  This felt like an ignition miss but inductive timing light seems to indicate good firing at all plug wires, even when held in gear & revved to 1500-1800 RPMs.  Plugs & wires repl <10K ago so not suspected.  Today the check engine light came on & I pulled down codes 25 & 26.  Reset it, drove it a little more & light back on--pulled down same 2 codes.  What is the most likely problem?  The Haynes manual keys 25 to lean malfunction & 26 to rich malfunction & lists trouble areas as: injector circuit, injector, oxygen sensor circuit, oxygen sensor, ECU, fuel line pressure, air leak/air-flow meter, air intake system, ignition system, mass air-flow meter, cold start injector.  That's a lot of items, so what should I do first?  Thanks for any help you can give.

Answer
These two codes are normally set by an engine misfire condition or a leak on the intake system or possibly an internally leaking headgasket or even a cylinder that may be low on compression. The first thing I would suggest that an engine compression test be done and if it checks good have an internal combustion leak test done to make sure there are no problems there, this is a good way to check the engine's health and you won't put money into some parts and service that may not be needed.