Hi and thanks for using 2CarPros.
The knock sensor is located under the intake and mounted in the engine block. Since the problem started after the work, my first guess is there is an engine vacuum leak resulting from everything being taken apart. A hose may have cracked, the intake may be leaking, or they may have overlooked reconnecting a hose.
With that in mind, you should contact the shop and express your concerns. Explain you feel there is a vacuum leak.
If you want to check for yourself, here is a link that explains how it is done. Also, I attached two pictures. The first is an exploded view of the engine, which indicates the sensor's location. Picture two is very specific.
https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
Let me know if this helps or if you have other questions.
Take care,
Joe
Images (Click to enlarge)
Jan 15, 2019 at 6:06 PM
