Zulfiqar: I doubt it's a glow plug since I changed out the glow plugs about two years ago, along with the engine wiring harness, resolving all the problems I had prior to that. As for a valve, very possible, but the lumpiness immediately goes away when the engine reaches a specific temperature. The lumpiness is there, then gone immediately. Also, if I raise the idle slightly with the accelerator--maybe 100rpm or less--I can make the engine run normally without any signs of hunting. Take my foot off the pedal when cold, and the hunting returns immediately.