Yes, back again for help.

[slideways...]

the ECU senses something is wrong and goes into ohshit mode. it will retard timing up to 20 degrees in an attempt to save your engine from whatever it thinks is wrong.

that sounds to me like it, or else one of your other sensors is malfunctioning.
incomplete combustion is also called "missing" and you should be able to feel it when driving(rough idle, rough acceleration, excess vibration in the motor).

[Zooropa1310]

Originally Posted by slideways...

the ECU senses something is wrong and goes into ohshit mode. it will retard timing up to 20 degrees in an attempt to save your engine from whatever it thinks is wrong.

that sounds to me like it, or else one of your other sensors is malfunctioning.
incomplete combustion is also called "missing" and you should be able to feel it when driving(rough idle, rough acceleration, excess vibration in the motor).

Anything I can do on my own about this?

[fugiot]

Yeah, it's got to be either the O2 sensor installation didn't go right, or your MAF sensor is bad too. It's a rare thing to have the MAF go out on you before the car is retired, but it happens.

Other than that, if you've replace the spark plugs and distributor, then the injectors are the only other thing I can come up with.