You can use Bosch scanner for Motronic systems or get flashing code by jumping green connector (if I remember correctly) in engine compartment. To be more precise that fuse box is located right before passenger side strut tower, it’s a black square box. Idle surge can be caused by multiple things, I would strongly suggest reading fault codes then repair faulty item and then proceed to idle surge. Most folks will tell you check this, check that, could be this, could be that...well that is no