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Hi all, as the title suggests I have an intermittent misfire in my car.

In my old 2.1 X-Type, I had a misfire that eventually killed the catalytic converter. I never managed to find which cylinder it was, although I'm pretty sure it was in either cylinder 1, 3 or 5 as it was the bank 1 cat that died. The misfire only really happened when the car was under strain in a higher gear such as going up a hill in 4th or 5th. Sometimes it was worse and sometimes it wasn't even there.

Now that I have my 2.5, I've found it has developed a misfire under the same circumstances as my old car. I decided to try and stop it in its tracks at the weekend and started servicing my car. When I pulled the inlet manifold off to change the plugs, there was a creamy gunk in the manifold in the pipe leading to cylinder 1. It would be what you would expect when water mixes with oil. I was guessing it could be due to some condensation forming and mixing with oil from the crankcase breather since it was the furthest cylinder from the air inlet? There was a very slight coating of oil on the rest of the inside of the inlet manifold.

After I cleaned the gunk out I changed all the spark plugs and the air filter. All of the spark plugs that came out were fine except the one from in cylinder 1. It was very brown as if it was burnt? On top of that, I plugged a code reader into the car and it said that there was a misfire on cylinder 1 and there was an error with the bank 1 catalytic converter. I've never had these codes before so it was a welcome surprise.

I decided to swap the ignition coil from cylinder 1 onto cylinder 2 in the hope the fault would follow it and so I could gain easy access to it if it turned out to be the coil at fault.

After I put it all back together, it started up fine and actually ran better. It felt a bit more responsive when I put my foot down. However, on the drive home from my dads warehouse I noticed the misfire again and it was quite a bit worse than before. This morning it was even worse again, the slightest incline on the way to work was causing it to miss a lot if it was in a high gear. I tried looking for codes again but there weren't any. On the way home I decided to buy a new ignition coil thinking it must be that ignition coil at fault. Fitted it tonight and to my surprise the misfire was still there.

So to summarise:
- Engine had a misfire, decided to service it and changed all spark plugs and air filter
- When I pulled the inlet manifold off, creamy gunk in the pipe above cylinder 1
- All plugs okay except in cylinder 1 which looked brown and burnt
- Code reader suggested misfire in cylinder 1
- Swapped ignition coil from cylinder 1 to cylinder 2 in the hope the fault would follow
- Misfire still there and a lot worse
- New ignition coil fitted to replace suspected faulty one, no change

I'm not really sure what to try now and I'm reluctant to throw more money at it... Any suggestions?

Thanks,
Chris
 
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