HC-SR04 Ultrasonic Rangefinder readings are off by a large margin

Question

I'm making a robot that should avoid obstacles and im using a HC-SR04 to measure distances. My problem is that my readings are off by a large margin. when there is no obstacle in the way I get a constant measure around 100 cm, but when I place an object in front of the reader suddenly it goes up to about 2000 cm. I've tried using the gpiozero library aswell, but same thing keeps happening. Is the reader damaged or what can I try?

import RPi.GPIO as GPIO
import time
import signal
import sys

GPIO.setmode(GPIO.BCM)

pinTrigger = 12
pinEcho = 16

def close(signal, frame):

    GPIO.cleanup() 
    sys.exit(0)

signal.signal(signal.SIGINT, close)


GPIO.setup(pinTrigger, GPIO.OUT)
GPIO.setup(pinEcho, GPIO.IN)

while True:

    GPIO.output(pinTrigger, True)
    time.sleep(0.00001)
    GPIO.output(pinTrigger, False)

    startTime = time.time()
    stopTime = time.time()

    while 0 == GPIO.input(pinEcho):
        startTime = time.time()

    while 1 == GPIO.input(pinEcho):
        stopTime = time.time()


    TimeElapsed = stopTime - startTime
    distance = (TimeElapsed * 34300) / 2

    print ("Distance: %.1f cm" % distance)
    time.sleep(1)