I think a big part of my problem is peripheral vision (hearing) of the front
sensors. As the car sped up I had to increase the frontdanger threshold. Now if the car gets turned a little to the left while running down the straight
it 'sees' the cardboard and turns left thinking that it is coming to the
corner. Solutions?

The simple one is to place the cardboard further away from the side wall.

I could rewrite the code so that hard turning left only is allowed when close to the side wall. Trouble with that is if the car ever got free in a room it would crash straight into walls.

I could add left side SRF05's. That would make staying in the middle of the lane easier and minimize the effect of peripheral hearing.

What do you all think?

Ken