Charade 1.0 sl 2004 engine issue

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Had a my car a few months now done lots of little bits and really enjoyed driving around especially with 48 mpg returned round town mainly.
How ever it has developed a new issue. It takes longer to start and is miss fire ring, revs are rough at 800 or dropping to 500 and bouncing back.
The left cylinder Coil removed stalls out engine. The middle removed car runs rougher but there is a popping noise from the back of engine, when the coil is connected. The right cylinder unplugged does not really make any difference. I've swapped coil packs and plugs and got same results.

Anyone else experienced this ??? cheers

Cheers Im trying to find

Cheers Im trying to find someone to do this for me at mo.
Im gonna reset ECU and Then plug in a fault code tester. As a friend is lending me one. Hopefully the tester will be compatable its a odb2 port I believe does any one know where the diagnostic port is Unknw ta

update

fault codes read 1 cylinda miss fire not telling which one
02 sensor Argghh! decided to change injectors in case thats why not firering. Now lost a rubber seal Sad The 10mmm 5mm 5.5 thick one that goes in block. anywhere I can get one ???? help
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