Probier es mal so:
Code:
#include <Bounce2.h>

int buttonPin = 13;
int sensorPin1 = A2; 
int sensorPin2 = A3; 
int sensorValue1 = 0; 
int sensorValue2 = 0; 

int motorPin1 = 8;        
int motorPin2 = 9;       
      
int motorSpeed = 0; 
int buttonState = 0;
int merker = 0;     

void setup() { 
  pinMode(motorPin1, OUTPUT); 
  pinMode(motorPin2, OUTPUT); 
  digitalWrite(motorPin1, LOW);
  digitalWrite(motorPin2, LOW);
  pinMode(buttonPin, INPUT);
  Serial.begin(9600); 
}
 
void loop(){
  buttonState  = digitalRead(buttonPin);
  sensorValue1 = analogRead(sensorPin1); 
  sensorValue2 = analogRead(sensorPin2); 
  Serial.println(buttonState);
  if (buttonState != 1)   
  {
    merker = 1; 
  }             

  if (sensorValue1 > 512 && sensorValue2 < 512 && merker == 1)    
  {
    motorSpeed = 1;
    counterclockwise();                    
  }

  if (sensorValue1 < 512 && sensorValue2 < 512  && merker == 1)   
  {
    motorSpeed = 2;
    counterclockwise();                    
  }

  if (sensorValue1 < 512 && sensorValue2 > 512)
  {
    motorSpeed = 0; 
    merker = 0;                   
  }
}

void counterclockwise (){ 
  // 1 
  digitalWrite(motorPin1, HIGH); 
  digitalWrite(motorPin2, LOW); 
  delay(motorSpeed); 

  // 2 
  digitalWrite(motorPin1, LOW); 
  digitalWrite(motorPin2, HIGH); 
  delay (motorSpeed); 
}