Before you guys fuss at me for not searching, I did, I really did. I found my two issues addressed separately, but together I am wondering if it could be something else.

1989 560 SEL 172,000 miles. Idle in park and neutral is about 1300-1400. In gear, drops to 700 or so and develops an intermittent 'roughness' and for some reason, seems to be rougher in reverse. Car runs great, just stopped at a light with foot on the brake, it gets rough.

I did try an idle control module from a salvage car, plugged it in and no change in the high idle in park, so I did not replace that.

Any suggestions/ideas are appreciated.

Sounds to me like an open vac line somewhere, which will speed up the engine. Of course, there could be other causes, but I would check ALL vac lines coming off the engine and elsewhere, unless beyond a check valve, as it the brake booster etc.

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)