On north American cars, try the PCV line as it splits open at the elbow.
Also check the spark plugs and the plug leads.
Run the fuel down, refuel at a different station, and see ifit continues. Sometimes you can get a bad tank of fuel, orget contaminates in your tank.
Could be in need of a tune up.
IAC (Idel Air Control Valve)
could be lots of things but have you changed you fuel filter lately?
It may be because the idling unit is broken.
Fuel filter.
You don't. It's all done by computer.
In a 2000 Ford Focus SE : That would be the 2.0 liter , Single Over Head Cam ( SPI ) four cylinder engine
Because your oil pump and/or oil pump bearings are dying.
I have a 2000 Ford Focus it uses Mercon V. Mercon V is what I use in my 2000 Focus with a standard transmission. I have an Automatic 2000 Ford Focus station wagon and the owners manual suggests Mercon V.
It sounds very much lke you have a leaking vacuum hose. Either it has deteriorated and needs replacing or it has come off its fitting. Carefully check the engine compartment in an effort to locate the source of the hissing sound. When you do repair or replace the hose you will probably cure the source of your idling (and hihssing) problem(s).
That would be the sound of your mother-in-law.
Consumer Focus was created in 2000.