did not have rough idle problem but I had "power" problem with my 83D.. would slowly leave a stop sign/light and not have power until I got up some speed. My transmission guy immediately (on the phone) referred to the trouble as a "low gear piston". I had never heard of such a thing, but he worked on it (replaced the piston) and everything was fine afterward. I don't remember the price I paid.. maybe less than $250?? Hope this helps.

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Nello Tare

1982 300D (266,001 mi.) looking and running great

Previously owned:
1976 450 SLC
1983 300D
1976 300D
also
1982 Jaguar XJ6 (loved, but gone)