New Problem With '92 Civic LX

My 5 speed Civic has begun, to mysteriously do the following:

It will not idle, at a constant RPM.

It will constantly fluctuate, between low rpm to high rpm.

I had a friend start it up; and then it began to do this. I thought first, that he was pressing the accelerator, in an off-and-on fashion. He stepped out of the car and it simply continued to rev up and down, from low rpm to high rpm.

What can the problem be?

Please help.

You have a vacuum issue. It’s either a simple vacuum leak, trouble with your fast idle thermo valve or your intake air control valve. Just google “honda surging idle” and you will be flooded with answers to this problem.

To see if the IAC valve is causing the surging, disconnect its electrical connector. Go to this link, scroll to the bottom of the page: