I'm surprised unplugging the MAP sensor didn't trigger a code, but that's
not important. The MAP sensor isn't the problem. It's sole function on
this vehicle is to detect EGR operation.
There's a remote possibility that the stumble is an issue that will be
solved by an ECM reprogramming. According to TSB 03-36-019, the reprogram
will address "infrequent minor engine hesitation after an initial cold
start (typically the first start in the morning)." The words that make me
think this may not solve your neighbor's problem are "infrequent" and
I doubt there's any issue that would require ECM replacement. This is
very, very rare on Hyundai. If I had to guess, I'd suspect a faulty air
flow sensor or an air leak between the air flow sensor and throttle body.