How do you idle down the RPM's on an '86' 420SEL? When I start the car, it is idled at 11,000. I read in a book somewhere that it should be around 6,000. The car seems to burn allot of gas. I mean, I do realize this is a large and older sedan, but when I tried to figure the mileage per gallon of gas, it's awful. Where under this great big hood do I look?? Can it be idled down without taking it to a mechanic?

Austin:

I assume you meant to say 1,100 rpm; not 11,000 rpm. You wouldn't want a 6,000 rpm idle either.

Check out the SEARCH facility. Key in FAST IDLE and only search the TITLE area for starters. There are many things that could cause a fast idle to include:

- faulty idle speed controller/actuator
- sticking throttle linkage
- TPS(throttle position sensor) out of adj.
- Vacuum leak
- Bad throttle switch
- Air plate position sensor

These a some of the possibilities.

__________________
Mike Murrell
1991 300-SEL - Model 126
M103 - SOHC
"Fräulein"

Wow, imagine a 6000 rpm idle!

Thanks! I kinda got carried away with all those zeros. I pulled a 12 hour tour and was kinda sorta dain bread. (brain dead)

As stated there isn't any adjustment! The idle speed computer matches the RPM imput to the engine speed. IF the idle speed stays around 1,100 then have the throttle switch checked out. This switch has a full load & idle contact. IF the switch doesn't close at idle then the speed will remain at 1,000 or higher. THIS is true only for 1981 to 1991 V-8 engines with CIS injection, like your car has.

__________________
MERCEDES Benz Master Guild Technician (6 TIMES)
ASE Master Technician
Mercedes Benz Star Technician (2 times)
44 years foreign automotive repair
27 Years M.B. Shop foreman (dealer)
MB technical information Specialist (15 years)
190E 2.3 16V ITS SCCA race car (sold)
1986 190E 2.3 16V 2.5 (sold)
Retired Moderator