Buzzing noise, loss of power when coasting to a stop

Intermittent problem, only happens when I'm pulling into a parking space or slowing below 5-10 mph about to brake to a stop. ABS-type buzzing noise that stops when I press brake or accelerator, then brake pedal feels harder. Also steering seems a bit harder while it's buzzing, almost like engine has died, but it doesn't die and no lights come on. Happening more often - several times/day, always under 10 mph.

Only other symptom is a couple hard starts, also intermittent - everything else ok.

Dealer cleaned throttle body, "reflashed" computer (these didn't help), and suggested air control motor (not done yet).