Originally Posted by Poolside
Regarding differences in injector flowrate; Injector mismatch primarily causes vibration and affects smoothness. But you're right, a difference in fuel flow between cylinders is one of the culprits that causes surging. But the fuel flow imbalance between cylinders is primarily caused by batch injection. I hope to get into that a little later. That and how it affects ignition timing.
It's interesting how much careful attention is paid to valves and throttles, getting the air intake right, and how little any of us know about FI matching. During all the modes (e.g. Cold start, warm up, accretion and high power) where the Motronic is open loop and the AFR is less than 14:1ish, fuel injector matching, acceleration) several percent doesn't matter for the reasons we've been discussing.
However during Closed Loop, when the average of the two cylinders is 14.7:1 (biased toward the richer cylinder a bit), the leaner cylinder can be in the 15s for AFR, creating added vibration, and Motronic induced closed loop surging. That surging could be especially true with an older, sluggish O2.
Lots of good stuff to get into here. Sometime we should go over adaptation values and their effects. But that's another topic all together.