Hello everyone

My 2005 CRD started smoking on the freeway and losing power and rattling/popping under acceleration. I pulled off the freeway and it was popping very loud with major power loss but still running. It would fire up fine and run but would pop very loud. I had it towed to a local diesel shop and they said it was popping back through the intake on cylinder 4. They have all the top end off and all the rockers and such they say seem fine. They say the first 3 cylinders are running smooth and the timing belt looks fine, don't know if they have actually checked the timing though. It has about 115,000 miles on it with original timing belt. They want to pull the head because they think there is something sticking one of the intake valves open on cylinder 4. Does this sound like the next step? They said the valvetrain looks like something on a porsche or space shuttle. Not sure that they are familiar with this engine enough. lol.
Could a glow plug have broken and be lodged in an intake valve?
Any help and knowledge will be greatly appreciated. I have been without her for three weeks and I miss her.