V8 Disco 1 can’t drive properly

[BenneB]

I have a 3.9L v8 disco 1 it’s not on the road yet but when you set off it sometimes drives fine but sometimes it’s like the throttle cuts out and puts the brake on, But then a second later comes on then goes off again and so on. I’ll be sat at full throttle and it just carries on doing this. Only when I stop. Put the brake on my self and set off again with it sort it’s self out. But only for it to happens again.
I’ve disconnected the cruise control ECU to see if that was interfering but that dosent seem to have made a difference.
Could it be to do with the speed sensor.
Anyone got any ideas? Or had this problem???