A foul smell is the most common sign of a bad catalytic converter. If you smell what seems to be a rotten egg and it gets stronger over time, the catalytic converter is not working properly. A large drop in your fuel economy may be a sign that your catalytic converter is going bad or is blocked. A lack of power, especially at high speeds, may be a sign that the catalytic converter is going, or has gone, bad.A vehicle that stalls during idle, or idles rough, may have a blocked or bad catalytic converter. Your catalytic converter may be blocked if you experience bucking or hesitation while trying to accelerate. Additionally, your vehicle may run at a higher than normal temperature. A catalytic converter typically doesn't go bad without an underlying cause. A mechanic should be able to find the original problem and may not have to replace the converter.
If your catalytic converter is going bad, that’s bad for the environment. And depending on where you live, that failing catalytic converter just might keep you off the road; a failed emission test usually means that you’ll have to before you can get your car back on the road again.
I own a 2003 Subaru Forester with 96k miles on it. the "check engine" warning light came on and the mechanic claimed that the catalytic converter was going bad. He turned off the warning light and told me of a inexpensive way to solve the problem. Run 5 or 6 tanks of premium fuel (91 octane in CO) the start using the mid grade (87 octane)instead of regular (85 octane). I've never heard of a fix like this. Is this true? Thanks.