Hi mate, not seen a reply to whether you've got it sort or not but from reading through the thread I've got another couple of thing you can check.
Check the throttle body for a ring of carbon and it doesen't have which can cause it to almost stick shut when slowing down.
Another possiblity with the throttle body is if it's solonide operated while you can see it get someone to turn the ignition on (but not start it) and you should see it open a very minuet fraction.
One other thing, not to sound daft but when you changed the plugs did you gap them correctly or put them in straight out the box? Even from new the plugs need to be correctly gaped with feeler gauges.
And one last posibility could be the throtte potenciometer in the accelerator pedal but you need to find out what the resistances are ment to be at different throttle opsition before reading with a multimeter.
Hope some of this helps 😊.