What causes a 2001 Ford Focus to shut off when stopped?

What causes a 2001 Ford Focus to shut off when stopped? - 1

Added (1). My daughter has a 2001 Ford Focus. It started shutting off every time she came to a stop yesterday. Today the engine will turn over but won't turn all the way on. We replaced the plugs, thermostat, throttle body, idle air sensor, throttle position sensor, mass air flow sensor, and put in a brand new battery. What else could the problem be? Had a mechanic look at it and he gave some suggestions but he's not 100% sure. We're going to try those but I wanted some other opinions also.

Stuff your arm down about as far as it will go between the engine and the firewall (engine cold!) and feel the outer part of the bend in the PCV hose. My guess is it has split - most do eventually - and that can cause all sorts of idle problems. It is more accessible from the bottom but the car has to be on ramps or jackstands for that.

The hose has two different size ends so you need an exact replacement part, not a length of hose.

No maintenance
Bad idle air control motor
Intake manifold vacuum leaks

We also had one. It did the same thing. One time it stopped in the middle of the high way but luckily we were close to an exit so my brother moved the vehicle by pushing it from the back. This was like in February. We ended it up selling it for like 1000$.

I miss that Focus.

But i don't know what the problem was. What color is your Focus? Ours was black.

It turns out it was a timing issue. It's too costly to fix considering how much we paid for it and how much work we've already put in it. So it's for sale for whatever we can get out of it and we just went and bought a 2016 Focus for the same amount of money we've already put into the 2001 Focus.

Can be a few issues. Often a weak fuel /air mix or slow idle control valve ( sticking) . Ideally a simple diagnostic check ought to pin point area that need attention. Just changing parts can be a costly and time consuming waste. If we have a breathing issue? Low fuel pressure? Etc that all ought to be found with a skilled technician and a diagnostic tool.