E30 Zone

This isnt a major concern of mine, but Ive noticed that when my engines hot and im sat in traffic (or more usually, McDonalds drive-thru) the engine revs tend to rise very slightly then settle again every 5-10seconds.

Assuming its ticking over at 650 rpm (?), the revs seem to rise to about 800rpm for a second or two then drop back down. It does this continually when its quite warm (half way up temp gauge).

Any ides?

could be the icv, give it a good clean out matey and go from there