Noise when accelerating...

The first "Ask My Dad" column reader question:

The car:
1998 Toyota Corolla
4 cylinder engine
175,000 miles
All scheduled maintenance performed

The problem:
For the past few years I've heard an increasing amount of noise (something
like a sputtering) when accelerating up a hill.  The problem has gradually
gotten worse over time and robs power from the car, resulting in me being
the slow car up the hill more and more often.  I originally thought that it
was a problem with the exhaust, but it continues to pass California's smog
tests with flying colors.

I once had the check engine light illuminate for a day and consulted the
manual and internet to determine that it was likely the catalytic converter
had failed, but it went out and hasn't come back yet.  I also had the car
scream a bit when started a few times, which I assumed was a mis-adjusted
belt.  Again, went away after 2 or 3 times (not consecutive) and hasn't come
back.