Flashing engine light, no power 2002 protege

Flashing engine light, wet, dry, hot, cold,
At idle, in neutral, feels like it will stall, give it gas and is better,
Loses power while driving,
This lasts for a few minutes, the light then remains on and all seems fine after.
Have had the catalytic converter changed, full tune-up.
any ideas? Im am researching for a neighbour,
Am waiting to see if any codes were investigated

Check for vacuum leaks. See if there are any cracks in the air intake hose going to the throttle body. Get the error codes, they should be a big help.

codes found p0300, replaced EGR, and,P0421, replaced catalytic converter, problem still persists?

P0300 is a random misfire. It sounds like the ignition coils are about shot. The tune up should have included spark plugs, so they're probably not the problem. The plug wires may be new as well. Ignition coil problems are worse when the engine has been running for awhile. When you shut down for a bit, it usually goes back to being fine. Check to see if the valve cover gasket is leaking oil into the holes that the spark plugs sit in. This can also cause a misfire. Hopefully it's the coils, otherwise it may be the computer. Replacing the catalytic converter for a P0421 is a bit extreme, the error is usually caused by a bad O2 sensor.

Taking it back in, will report on findings,

Thanks