I would start with an injector cut-out test. Just crack the line at each injector one at a time with the engine at idle. If you get to one that doesn't change the running of the engine when you crack the line, you've found your problem cylinder. After that, swap the injector with an adjacent cylinder to see if they problem follows the injector or stays with the same cylinder. If the problem goes with the injector, you know the injector is bad. If not, then you know it is something else.

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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.