love this car.but a few issues unfortunately.the most pressing being cold starts.all glow plugs are working and resistance is on spec but its clear one cylinder is misfiring with a thud every few seconds.after warmup it runs and pulls smooth with lots of power. however at idle i do see a little white smoke of the unburned fuel variety.at least thats what my nose tells me.using the glow plugs as pyrometers hooked to my ohmeter i observe cylinder#5 is burning cooler than the others indicated by higher resistance than average.i have a bosch pop tester and utilized this to check injection pressure and spray pattern which is good on all injectors.i pulled the intake manifold and checked all the intake ports which like the manifold were covered in a thick layer of black goo which i proceeded to remove with varsol.reassembled and restarted with no positive effect.where do i go next??does this look like the symptoms of a valve ,ring or sleeve problem?