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The PO421 is a catalyst efficiency code during warm up. That's an indication of a weak calalytiic converter and it will probably have to be replaced soon.
The PO171 is fuel trim lean bank one. that means there is a lean condition and the computer has adapted as muct as possible. Look for whatever is causing the lean condition. It could be a vacuum leak, a dirty or bad Mass air flow sensor or possibly even a bad O/2 sensor among other things.
It could if it had one. That car uses a Mass Air flow sensor instead of a MAP. That could be the problem. Try cleaning it with carb cleaner inside.
If you don't give us the right information, you don't get the right answer. Transposing those 2 numbers makes a BIG difference.
Check for vacuum leaks also for the other code.
That's very possible. Check the rest of the intake snorkal also for any cracks or holes.
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