Megane rs 250 missfire :(

the brown is of course light rust from ingress of water passed the coil pack, clean and refit

 

Awesome. I thought it might be but I'm bit paranoid, since clio, of pistons eating them selves.

Done and done

 

I’m going to bump this thread, sorry!

I’ve had the same issues as a few of you. While accelerating hard and then changing gear it ran like crap until I let off the throttle but now I can’t even accelerate past 3k without it doing it, almost feels like the cold cut limiter coming in way too early. I’ve changed the thermostat and the spark plugs but it’s still doing it. Coils look fine and it didn’t detect a misfire while driving.

The next step is either trying new plugs in case these ones are faulty and doing a compression test. Are there any other issues that could be causing this?

 

I would try O2 sensor - mine was similar to yours as it got worse. Changed that and it was fine.

Although....mine is an r26 it does have the Mk3 engine - and that has recently blown a ringland and piston - it wasn't suffering from the issues you have beforehand, just felt sluggish and down on power, no trouble revving. But a compression test never hurts. May put your mind at ease, its a 30 min job either way.