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New issue: 280SE engine races on startup

Started by Feather535, 09 October 2022, 03:50 PM

Feather535

It's been a while since I've started the 280SE I rescued because I've been doing other work on it.  But today when I started the engine, it ran rough at first, then raced to about 4000 RPM. Kind of alarming! The rough idle on cold starts needs to be addressed, but it was like that before.  The racing is new.  I shut the engine down right away when that happened, but tried a couple more times and it did the same thing.  The throttle plate appears to be fully closed, the linkage isn't binding, and I don't see any disconnected vacuum hoses.  What could be causing this?
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1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

Randys01


Feather535

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1977 280SE
1983 300D (sold)
1988 BMW 535is
1999 E320T (sold)
2009 E350T (wife's)

rumb

Look at the linkage that goes down from the air flap to the actual throttle plate below.
The air flap is up top where you can see it, but the throttle plate is actually below where you cannot see it.

The other thing to look at is the cold start valve possibly stuck open?
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,
'16 AMG GTS
'21 E450 Cabrio

raueda1

I'm thinking some kind of throttle linkage issue too.  The thottle linkage functioning and adjustment is described here on page 2.  Pictures are terrible but you can probably puzzle it through when looking at the actual car.
https://cdn.w116.org/tech/K-Jet_Diagnosis_Adjustment.pdf (on this site).
-Dave
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0

SteveDuNord

When this happened to me, it was the linkage caught on something that I'd previously fiddled with. Double check!
'77 280se

daantjie

A good opportunity to lube all linkage and pivot points.
Daniel
1977 450 SEL 6.9 - Astralsilber