I think I may have found how to sort my specific issue (MS43 / M54 / MT with no Clutch Switch in E30)
I've been playing with the TunerPro since yesterday and found this which sounds like it's slowing my Throttle closing, and one of the conditions to not have this interfere is the Clutch being pressed. Since I don't have a clutch switch sensor, it's always going to slow my throttle close. I'm just disabling it now and loading the bin file. I was already playing with other stuff and reset my adaptions, so going to have to go for a bit of a drive to let it relearn things and see how it goes.
Lucky for me it's a nice day
https://www.ms4x.net/index.php?title=Siemens_MS43#Throttle_Request_Correction
Throttle Request Correction
To provide a smoother driving experience the ecu will limit how fast the throttle can close based on the current engine load.
If the clutch is not pressed and the requested throttle setpoint is larger than the value specified in c_tps_req_ltc_min or smaller than the value specified in ip_tps_req_ltc_min_[gear] the throttle setpoint closing rate will be limited.
When the ecu starts limiting the throttle setpoint it will be decremented by the value taken from ip_tps_req_ltc_lgrd_[gear] until the following conditions are met:
The limitation duration specified in ip_t_tps_req_ltc_max_[gear] has expired.
The requested throttle setpoint is larger or equal to ip_tps_req_ltc_min_[gear].
The limited throttle setpoint is smaller than the requested throttle setpoint.
The clutch is pressed.
If any of those conditions are met then the ecu will use the requested throttle setpoint and will not start limiting the throttle setpoint again until the time specified in c_t_dly_tps_req_ltc(0,85s) has elapsed.
The id_tps_req_ltc_gear_[gearbox] tables controls if the throttle request correction should be active depending on the current gear. To disable the throttle request correction function set the id_tps_req_ltc_gear_[gearbox] tables to zero.