I second the EGR. If your cat was bad, the CO and HC would probably be much worse. EGR controls peak combustion temperatures and NOx formation, so faulty EGR would be the prime culprit for a NOx fail.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 401,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 26,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.
99 Mazda Miata 183,xxx miles.