1996 Jaguar XJ6 Check Engine Light and performance

Engine Performance problem
1996 Jaguar XJ6 6 cyl Two Wheel Drive Automatic 192K miles
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My Jag xj6 runs rough.

I recently replaced two Ignition spark coils and all 6 spark plugs.

A mechanic friend then pulled 2 codes (1313 and 1314)

I believe he said that the #3 fuel injector needs to be replaced and also the air mass flow meter.

I would like to avoid just buying parts until the car runs like it should.

Would you please tell me what to do in order to get the car to run smoothly.

I can drive it but the check engine light remains on and it runs like it is only running on 5 cyllinders.(rough)

Another shop said it might be a head gasket, which doesn't make sense to me, but I am not a mechanic.

Please advise.

Thank you very much for your time and advice.