Bad ECU 1.6 8v 1990.

[fixkick]

let me explain backup mode
it is when the main ECU goes dead. (the main brain, and all features, dies)

there is a smaller, very very very crude, ecu (or other chip), that wakes up, ( with CEL dead is the only clue, stuck on or out)
this crude mode, runs fueling in a very crude way. (gets you home maybe, some report engine love to flood out and stall in this mode)

RPM and TPS throttle angle may be its only way to calculate fueling,