[galileofigaro]

You can feel the engine running normal and after a couple of seconds slight revving increases for 2 or three seconds, then comes back to normal.
At a red light you can also feel it, specially when you press the break pedal you have to press it a little harder to avoid the car from going.
At idle speed goes normal, then increases speed very little for a few seconds then back to normal. All this is constant, happens al the time I have the engine on.
I changed the idle control valve but problem remains.
Thanks a lot

 

[Leora83]

Vacuum leak. Easy diagnosis, hard to find the specific location. Start with the PCV hose, because it's a known culprit. Given the car's age, if it hasn't been replaced, then it's time even if it looks okay.

Usually the IACV causes high idle, not fluctuation.