My mechanic replaced a idle air control valve on my car because it was accelerating on it owns but it still didn't fix the issue?

It's a 2001 Ford Focus what else could be wrong?

The car is too old. Junk it.

Start with adjusting the throttle cable so that it's got a bit of slack in it.
Clean the throttle body.
If it still won't idle find a mechanic with a scan tool that can read the engine data to make sure all the sensors are working with in spec.

Possibly it''s due to a bad TPS sensor but could be other issues such as vacuum leaks, sticky throttle linkage/cable/pedal, etc… Better try another qualified mechanic/shop that can diagnose it properly and perhaps get a credit for the wrong diagnosis/part.

Tell your mechanic to return the IAC valve and repair the vacuum leak at the rubber elbow where the PCV hard line attaches to the PCV valve. They all deteriorate there and cause your problem.

This sounds like engine either has wrong fuelling /timing and a diagnostic check can sort or more likely we have an engine burning oil ( pull over) . We also need to check for simple faults such as carpet not fouling throttle? Throttle cable not sticking etc
a decent garage ought to be able to find root cause after a few checks.