Sorry I’m late to this one. Right from the first post I saw a bad cat. It’s almost impossible to get the HC’s down below the required limits without a good working cat. However I wouldn’t say it wasn’t working at all or it wouldn’t pass at cruise (2500 or higher). When cat converters get hot they “lite off” and start burning the unburned HC’s. When they are “fresh”, once they start off they’ll keep burning regardless of engine speed. When they get old they tend to shut down at idle (that’s why they do both cruise and idle tests). Sounds like that’s what yours was doing. Once you don’t have to have pass emissions any more, pull the cat out and have a straight pipe. You’ll love the sound!

Well, that's good. I once had a cat converter break down to the point that it clogged up and turned cherry red. Could have destroyed my engine if my mechanic hadn't noticed it in time. Was causing the engine to run rough.

I did not suspect the cat initially because it was only about 6 years old, and it looked fairly new from the outside.
When I got it off, I swear it looked just as good inside as the new cat.
After talking to my mechanic, here is what we think happened. A few years ago, I suddenly developed really bad compression in all cylinders on one side of the engine, and I drove it that way for a long time. My mechanic thinks this probably damaged the Cat.
I got a valve job done on that head only recently. It looked like I had dropped several nuts in the engine or something as several of the valves and seats had big gouges taken out of them. I do not know how it happened. I am thinking back to how my (then) three year old son liked to satnd in the trunk and watch me work on the car when I put reconditioned heads on initially. Maybe he dropped some bolts in the intake while I wasn't looking.

[This message has been edited by sd_iconoclast (edited 11-30-2012).]

Thanks for sharing your "fix".
Many times, threads will just fade away, and we never hear what the resolution to a problem was.

quote Originally posted by Rodrv6: I had issues with high HC on a Fiero for several years. Tried the usual stuff (mostly mentioned above) and finally replaced the catalytic convertor, which dropped the HC readings well below the upper limit. If the items listed above don't help enough, you might consider doing the same thing.........

Wow, I was actually on to something! (Doesn't happen often, so I need to celebrate)

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Rod Schneider, Ball Ground, Ga.
"You can't have too many toys!"
1988 Fiero GT
1987 Porsche 944S
1985 Porsche 944
1966 Porsche 911
2001 Chrysler 300M
Van's RV-6 airplane-at the airport, nearly ready to fly