engine revving on its own?
 

89 Porsche 930, took it for an oil change, then wand car wash. On my way home from the wash to store it for winter (cold day, around 38-40 degrees fahrenheit), I approached a red light, stopped, and put it in neutral to wait for the green and noticed a funny thing:

Every 1-3 seconds the engine would rev itself/spike momentarily from the normal 1000 RPM idle to around 1500-2000 RPM then quickly back down.

This was not happening (to my eye anyways) while in gear and driving, although it may have been and just not that noticeable.

I ran it by my mechanic, he's not quite sure and recommended parking it for winter to look at in the spring on first start.

Any thoughts?

Your car has CIS Fuel injection. I colder weather, you sometimes get some surging. A slight mixture adjustment may be all you need.

An Italian tune to dry it out and blow the cobwebs out, and it may fix this problem. As the guy said it's not a major and may as well wait until spring if the hour of heavy duty driving it doesn't clear the moisture out.

This thread is informative. https://forums.pelicanparts.com/porsche-911-technical-forum/185926-its-time-year-again-cis.html