380 idle lowers in D
 

My 85 380SE (198k) idles at about 700 in P but drops to just above 500 in D. It idles smooth in both, has normal power, etc. Any idea what to look at? The only reason I care is that the temp goes up at a stop after freeway driving unless I put it in P while I'm stopped esp with ac on. TIA, Jim

it would be normal for it to drop some. 200 rpm seems a bit much.

tom w

Do a search on idle control valve. They get dirty over time and can affect your idle. Normal idle in drive is around 600, so yours is not way off. The auxiliary fan might not be working.