Problem with idle

[cccp]

My idle is really odd. really really odd. 95% of the time it idles perfectly, right at around 700 rpm. However every now and then the idle will either fluctuate like crazy, (bounce between 700 and 1500) it does this very smoothly, as if I am giving it gas then letting off. It'll do this for a few minutes then just stop.

Also sometimes it idles at crazy rpm. Sometimes itll idle at 2000, sometimes at 2500, and today twice it idled at 3100. I drive an 87 eta. What the hell is wrong with it? Thanks in advance

[KenC]

Clean your throttlebody and your ICV.

[m42rowe]

check all of your vacuum lines, if one is craked it might cause that.
hope that helps