Discussing this point tonight with another TM member, we concluded that if the FBW link between throttle pedal had any lag it would simply slow the revs rising but not cause a misfire. In my case all came good with some boot and load on the engine, and issue was only on very light throttle low speed conditions. Worth following up though if issue happens again.
As mentioned earlier it was interesting to see the throttle range dial I'd configured on my OBD Torque app when connected to car via bluetooth link to OBD2 dongle. With just ignition on the dial, starting at 17%, followed pedal movement. As engine not running the stepper motor driving throttle butterfly could be heard following suit.
Had an issue many years ago with Val's Shogun Pinin which also had FBW throttle. Car went into limp mode with MIL light on, and barely allowed us to get home, although don't recall any misfiring. Fault found to be sticky throttle spindle such that stepper motor couldn't react and cured by exchange throttle assembly.
According to Roadster engine schematic there is a stepper motor actuating butterfly to open or close throttle and controlled by position sensors which also control the ECU power demand loop. I would imagine if stepper motor fell out of kilter with position sensor this would throw a MIL warning and probably trigger a limp mode as above.
