Just a WAG but in addition to Hit Man X's good suggestions, what about the idle air control solenoid right in front of the air cleaner box?

The 560SEL/SEC vehicles are well known for a high idle problem that can occur at higher miles on the car

The mechanic notes said in part:

"A check with an ohmmeter showed an intermittent connection to the solenoid ~~~ 5 ohms or infinity, depending on where I banged the unit with a rubber hammer, (after removal from the intake manifold). Since it was bad already, a dremel was used to grind off the lip that had been bent in to hold the connector in place.

After gently pulling out the connector, a broken lead was revealed from one of the connector pins! A few minutes with a soldering iron and some cafeful application of 5-minute JB weld and Jim's car idles at 600-700 RPM. Don't throw away those old $250 solenoid air valves, they might be repairable."


( This was done at 90,500 miles/13 Aug 2001, --- just before the 9/11 attack ) ... the car runs perfect ever since, this trouble never recurred, and the vehicle is now at 168,000 and over 8 years later....)

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1991 560 SEC AMG, 199k <---- 300 hp 10:1 ECE euro HV ...

1995 E 420, 170k "The Red Plum" (sold)

2015 BMW 535i xdrive awd Stage 1 DINAN, 6k, <----364 hp

1967 Mercury Cougar, 49k

2013 Jaguar XF, 20k <----340 hp Supercharged, All Wheel Drive (sold)