advice on high rev, cutoff issue
 

I purchased a Chevy Express 1998 5.7/350 V8, but the owner says the car has the following issue.
The car rev too high when idle, and sometimes cuts off completely when put into neutral. He changed the mass air meter sensor and the air intake sensor, but no avail. What do you think the next step should be. Should I just take it to any mechanic, or should it be one who specializes in specific parts (engine, transmission, whatever).
I don't know much about cars, so I'm just trying to get a basic idea.

Welcome to the forum...

Have you check for vacuum leaks at the intake? checked vacuum lines and the brake booster?

yes he did.

I would do a double check with some carb cleaner, with the engine running spray in sample spots to see if the idle changes with the spray to gasket areas and vacuum fittings....

Make sure the throttle linkage not hung up and moves freely

check the idle air control valve for proper operations

Use an OBD reader to see if there are any codes stored...