I once saw a civic that was slowly revving up and down while it was idle. A friend told me that a performance camshaft will do this. Anyone know what causes this?

 

lol..A cam won't do that. Usually the iacv causes it

 

Yea idk how he figured that but whats going on when this happens

 

The iacv is dirty usually. Search it and a bunch of threads will pop up. It's not something you want your car doing, if that's what your asking

 

Yeah a car with a big cam sounds way different than a dirty IACV. you tube has a lot of videos of both.

 

Yea usually its a dirty iac valve. You can pull it out and clean with some brake clean/carb cleaner. Or just replace it.
This problem may also be caused by a vacuum leak. Leaking intake gasket. Be careful and make sure your ignition wires Arent arcing and spray brake clean around the intake a see if u notice a change in idle. If you do sense a change, theres your leak.
Hope that helps