revs

Sorry if this is a stupid question, I'm a complete novice, changed the fuel filter, first time doing anything like this. Basically I've changed the fuel filter, and now it's doing something I've never noticed before, when it idles, the revs have one single little hiccup where it drops below...

HI i'm a newbie when it comes to Honda cars and not having a good start, so hoping for some comfort and info.. i have recently bought a 2nd hand Honda Accord 2.2 ICDTi but have an issue with the coil light which has just come on. I drove it this morning without any problems on the motorway...