I was asked to look at a Clio 197 cup with a misfire but only had time today and it is fixed now so just felt like sharing to help point people in the right direction as so many have the problem and you don't always get the answer. Problem: When the car is cold ran fine as it warmed up a misfire our loss of power more accurately began to happen under acceleration. Idle was not noticeably off but pulling away a bit of spluttering loss of power which could be managed by bringing the throttle in very gently so that's the problem. Diagnostic: With the Renault Clip no errors came up, the upstream lambda was reading a little different but that was more a symptom than the problem. So basically no error codes no warning lights on dash no errors with live data on the clip which I was expecting as I have seen injector and emission warnings before with other Clio's but this problem seems to fly under the radar. The car was in the middle of going to a new home so I was suspicious of everything but nothing obvious in the engine bay or wiring or unplugged sensors. Fix: Looked around the head small bit of oil around the coil pack next to the VVT solenoid so first job unknown car to check for oil in the spark plug holes. No oil in the spark plug holes but signs there had been in the past as well as signs of a lacquer around the rubber ends on the coil packs from previous engine dressing or silicon spray at some time. Now the way I identify the cylinders is that 1 is nearest the timing belt and 4 is nearest the flywheel so the #3 plug had obvious signs of spark damage on the plug's hex base. So the next step from what was found bad plugs and or coils so with my car sitting there I swapped the coils and plugs across and the problem was solved with a quick run up the road so next I swapped the coils back to the original ones and the problem appeared so the problem was with the coils as the plugs were my good set. Now to find how expensive it was going to be I put my good number 3 coil pack back in the problem got better but there was still a problem so looking at the used plugs the #1 plug looked similar in appearance to the #3 problem plug so I swapped the other good coil pack into the #1 cylinder and the engine ran fine. So two coil packs were needed #1 and #3. Now nothing great done and no medals handed out but you can have a faulty coil pack or two with no warning lights and no obvious signs visually or with diagnostic tools resulting in a loss of power or misfire under acceleration with a normal idle and stationary revving of the engine. I hope this can help someone else in the future to go ahead and carry out a repair. The car had second cat removed and I think a Miltek exhaust to be honest I was thinking along the lines that someone had mapped and modified the car then striped it back to standard to sell on so I had been thinking the worst.