throttle position sensor

Hi guys i have a 2002 vw jetta TDI and I've been noticing something strange. When I go at a steady pace my rpm will bounce from a low rpm to high but its very small difference but you can still feel it when driving it. Do you have any idea's on what it might be? I think it's the throttle position sensor but just not sure?

Manual or auto? If manual it sounds like the clutch might be slipping a bit

... I'm going to guess it's an automatic, and that the issue is often noticed when the tach is around 1900 RPM. Well documented on here... something inside the auto trans, not sure if it has been narrowed down to always being the same root cause. Some recommend (auto trans) doing several fluid changes in rapid succession- sometimes helps / fixes the issue. The auto trans in this particular vintage has quite a reputation- search 01M