Car model: AE86

Engine type:16v bigport

Problem:
car has a massive flatspot only when in 2nd gear. when going straight from 1st to 2nd or around hard cornering in 2nd it just spits and burbles no matter how hard to put the peddel down it just keeps doing this for about 5-10sec. but when the clutch is ingauged it stops then goes fine in 2nd untill you go back down below 2500-3000rpm it does it again. it only starts to happen with the car is heated up and only around 2500rpm and up.

i have replaced the plugs with bosch p3-4 platinum plugs and a bosch GT40 coil. the leads seem fine, cleaned out fuel and lines, fitted new fuel filter, filled with shel premium 98 and it hasnt changed.
i am going to book it in with a local machanic this week but id rather fix the problem with your help and ideas before i go throwing my money at the high priced machanics we have here in warragul!.. ill get a video of this today and post up hope someone can help cheers! Benny