Can moisture or water in gas cause a rough idle or a low knock to trigger a knock sensor?

Hi,

If you suspect there is water in the fuel, it can cause a few different things. For example, it can cause a rough idle, a misfire, power loss, stalling, hard starting, and will likely damage the fuel pump/system if not taken care of.

As far as the knock sensor is concerned, it can cause a problem if the engine's combustion is off. In other words, the air/fuel mixture is not where it needs to be. That can be caused by moisture. When the air-fuel mixture in the combustion chamber doesn't ignite properly or combusts unevenly, it can create pressure waves that cause a knocking sound. This knocking is recognized by the knock sensor which adjusts ignition timing to eliminate the knock.

If you suspect there is water, I recommend purchasing a fuel additive from a local parts store that is designed to eliminate moisture in the fuel tank. The one that I know of is called "Heet". See pic below.

Let me know if that takes care of the issue or if I can help in any way.

Take care,

Joe

See pic below.