Which one(s)? Is there a particular circuit I should look at?

Today, my 1999 V70 abruptly lost power. At idle, with the transmission in P or N, the engine lurches back and forth between about 700 rpm and 1200 rpm. In P or N, I can rev the engine by pressing the accelerator. In gear, there's no throttle response whatsoever. The idle continues to oscillate, and ...