Just got back from a road trip: Denver--Flagstaff--LA--Denver in the 85 TD. Ran very well most of the trip. On the way back today got a very rough idle. I'd climbed eastbound to the Eisenhower tunnel in 3rd gear 62mph, about 4000rpms. Ran fine. Coasted downhill the other side for about 10 miles, rpm's at about 2000, no pressure on accelerator. Ran into a traffic jam and slowed down. The idle was horrible. Shook the whole car. Had to keep the rpm's at about 1100 to smooth it out. Stuck in the downhill traffic jam for about 10 miles, idle still bad. Climbed Floyd Hill under full power just fine. Coasted down to Mile High and drove at about 65mph about 10 miles home. Idle is now fine.
What caused that very bad idle? Some dirt in an injector(s) that blew out once I powered up again? Your thoughts.

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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