Your lancer has a cable throttle, the sensors only report how much the blade is opened by your foot, in your car, the motor is commanded to achieve a certain rpm, thats why I asked to put the car under load on open road in first gear only.
Btw
The disa diaphragm is not the O ring, its internal to it, any diaphragm leak on it or a ccv leak will throw lean codes on both banks in your car, your ecu splits the engine into two banks, 123 and 456, its tuned like any other otto cycle engine with a throttle body infront of manifold.
Meaning, basic vacuum gauge inspection and testing for leaks. The valvetronic ones require a completely different approach.
A bad disa wont cause surge, and neither would a dead ccv, however a flapping throttle due to a duff MAF sensor will cause flapping in a lot of cases.