Misfire

Hi don't know if this is in the right place on the forum. Took car for mot today passed with no advisorysI know it's french lol. So treated it to a wash went to drive it of the drive and tick over was lumpy. Then it started missing only at low revs so drove it a little while and it was missing. So pulled up with it running and ever now and then a small misfire. There is no management light on so took it to my mates garage and he plugged the machine into it. No fault codes even swopped the coil packs still the same. He seems to think that one of the plugs as gone down. As if there was a fault is machine would read it and all is fine on is plug in machine. Any help on this guys or ideas would be a great help thanks