Uneven idle in 2010 Jetta TDI

Hello all,

I had my car in park with the engine idling when I noticed a slight variation in the sound of the engine idle. The engine made a sound as if the idle speed was alternating between a slightly raised idle speed followed by a lower idle speed. This pattern repeated for over a minute with the higher speed/lower speed intervals happening regularly every one or two seconds. So the high speed intervals were of the same duration as the lower speed intervals and were spaced evenly over time with sort of a rhythm. The difference between the higher idle speed and lower idle speeds were also very slight but were definitely noticeable and audible. As mentioned, after about a couple of minutes the engine went back to a steady even and normal idle.

Can somebody please tell me what would cause this and what potential problem this may lead to?

Thanks in advance for your help.

Regards,

Was the A/C on? If so, normal.

Possibly the car was finishing up a regen.

Sounds like normal operation if it went back to normal idle with no check engine light.

Thanks 94X, all seems well now.