Struggling with emotional wellbeing of our (potentially) autistic son.

We had always had our suspicions, but last year our son's primary school teacher said she would like to refer him for testing. Now our son is (mostly) ok with changes in his daily routine, however he struggles with controlling his emotions, whilst I know a lot of children are emotionally sensitive it can be as simple as him having tomato on his pasta, which is normally cheese and tuna pasta , that causes an outburst for him to start kickin, punching, slapping, spitting his mother and I. We are terrified to take him out into the town incase the wrong bus turns up or the bus is running late as these are his biggest triggers. before now my wife has forcibly held him in her lap to keep him calm. We are running out of ideas on how we can help him control his behavior. We have tried the temporary removal of his toys, sending him to his bedroom, the naughty step. Nothing seems to alter his behaviour because no less then 10 minutes out of his punishment he is acting up again. Has anyone had experience with this and how can we curb it?