2003 Escape XLT 150K miles. Randomly while in gear stopped at a light (all warmed up) - the RPMS will drop way low and then surge - up / down - up / down.
Pressing the gas pedal does not get snap it out of this loop. But after a minute or so, it levels out and idles / runs normally. During the surging, you can smell gas.
I had a 2004 Sport trac that did the same thing. In that case I replaced a small hose going into the PCV that was cracked and that seemed to help.
I am assuming that it is a sensor or vaccum leak. I havent tried to clean the throttle body yet. Anything simple / common that may be the cause?