Can someone explain the button under the loud pedal ?
 

Is that for the overboost? Sometimes my car runs very very well and sometimes it feels blah? How do you make sure the overboost works every time?

Is it a button or stop?

It's just a stop.

After a closer look that's what I had thought. But I still am not sure how overboost is called apon? It seems to only happen 40 percent of the time. But when it works it's noticeable.

Overboost is provided by the ECU and it depends on the RPM and throttle position switch position, i.e. wide open throttle. Overboost is only provided when appropriate and even then only for a maximum of 15 seconds.

http://12v.org/urs/BoostAndOverBoostGraph.jpg

http://12v.org/urs/throttle_position_switch.jpg

Thanks that helps a lot. There needs to be a full load switch.

I'll let the boys at Bosch circa 1991, via my way-back time machine, of your concerns. ;)

That's the spirit.

So when the car gets a custom chip can the tuner change the overboost? Or modify it? Or do you need to go stand alone em?