Hyundai Repair: 03 Hyundai sonata, mass air flow sensor, mass airflow sensor

Question
QUESTION: Good Afternoon,

I have an 03 Hyundai sonata w 75K miles.  My car at times gets sluggish and has problems accelerating.  This seems to always happen on the expressway.  I took this in for repairs at the dealership a yr ago for the same issue.  They changed the sparkplugs, wires and crank sensor( said this was the cause).  However, almost a yr later after spending $800, Im still experiencing the same problem.  I took it back again, and they test drove it(Im guessing to the STOP sign) and found nothing wrong with my car and sent me home after charging me $100.  Oh, by the way No engine is present.  On my way home on the expressway it started again.  Luckily I had someone following me in case this happened to prevent in accident.  I took it back and another tech test drove and experience my concern.  They then determined it was the Mass airflow sensor.  Once that was changed they test drove it again thankfully and stated the problem is still present.  Tech is now stating its the MASS Airflow sensor and the catalytic converter.  Is this the solution or a temporily fix for another major issue, maybe the engine.  Dont want to be nickled and dimes again.

Thanks

ANSWER: Without checking the car, it's difficult for me to offer an opinion other than it's plausible that this issue is caused by the catalytic converter.  If it is, replacing the converter should fix the problem permanently (unless another unrelated issue comes up).  If not, it won't change anything.  

Another plausible cause of the condition you describe is the fuel pump.  Low fuel pressure and restricted exhaust (e.g. clogged converter) can have very similar symptoms.

---------- FOLLOW-UP ----------

QUESTION: Hi, its me again!  Is the mass airflow sensor and the O2 sensor one and the same?  If not, could this also be an factoring issue?  Just wondering since my check engine light never came on at any time to identify the existing problems.

Again thanks for your help.

Answer
The mass air flow sensor measures the amount of air entering the engine.  A faulty air flow sensor can cause the conditions you describe.

The O2 sensor measures the oxygen concentration in part of the exhaust.  Depending on your engine, you may have either two or four O2 sensors.  It'd be very unlikely for a defective O2 sensor to cause your symptoms.