I've a similar symptom on my 85 300td. Starts right up, runs fine for about 20-30 seconds. Then it hiccups. It's jsut a small hiccup but you can tell it is there. This lasts for about 30-45 seconds, then it smooths out. I replaced the glow plugs and it made little difference. It's not a big problem but I would like to understand what is happening.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13