[Doubledip]

Can also be leaking injectors. lift the rail up after undoing the 4 bolts and switch the ignition on to prime the fuel pump/rail and look at that corresponding injector to see if fuel is pooling. Also it maybe worth your while to invest in a spark checker and then test each plug lead etc... (this device makes the coil push extra hard to jump the big gap and is simple to use) - should be able to pick one up from any decent auto shop.