Euro 280sl cold idle

[knarf]

Greetings Forum Members,


Does anyone know what the cold idle speed should be for a 1985 Euro 280sl?
My car cold idles just under 1500 rpms in park, then gradually drops to around 750 rpm at normal operating temperture.
If I start right out driving the car in city traffic I almost have to "ride" the brakes for the first 5 - 10 minutes to control my low speed driving.
Is this normal for this car with no distributor vacuum retard?


Thanks,

knarf

[ericgr]

If this car has an idle control valve like my 380sl, you should clean it, test it, verify the electrical connection (unplug it and see if the same if so connection or valve is bad) and may need to be replaced. My car also has a warmup regulator. Because your idle is so high at warmup it sounds like the valve . If the connector is bad you can make a ew one with those butt end connectors at the parts store, crimp one end and slide other end onto valve.

[knarf]

Ericgr,


Thanks for the reply.
I'll diagnose as suggested this weekend.
Unfortunately it's the only time I have to "tinker", after work,
with the shortened daylight hours.



Knarf

[MrCjames]

I am not at all familiar with Euro-spec M110 of that era, however, I would imagine that the auxiliary air slide (used for warm up) remained until the end of production. With that high of an idle I would suspect the “auxiliary air slide,” mounted to the side of the block under the intake manifold, is your culprit. It will have 2 rubber hoses attached to it. One hose draws air from the forward side of the throttle plate (between the CIS mixture assembly and the throttle plate) while the second hose routes the air to the under side of the throttle plate. A preset metered opening determines the idle speed; a larger opening = higher RPM’s, hence the increased idle during cold start/warm up. With the engine speed you are referring to I think I would look at this device should you discover it is fitted to your vehicle. I am almost certain it is even with my limited Euro-spec knowledge.

[GermanMarque]

Don't know if this helps, I've got the 110 6 banger 280SL with the 5 speed box. At startup, it will always idle fast around 1500 rpm, before dropping back to 600rpm when the temp guage hits under 40. It normally only takes a block to drop and obviously isn't a problem with the manual. The handbook claims this is normal.

[ctaylor738]

Being blessed with two 280SL's -

One goes to about 1200 after firing and immediately drops back to 750.

One goes to 1100 and gradually drops to 650-750 as the engine warms.