Poor/low idle M102 when re-starting after hot?

[derin100]

On my C124 with the 2.3L M102 it's had an annoying tendency after a decent length run (so that the engine's warm) and then switched off to idle too low/stall when switched back on again.

This quickly resolves once you've got it up and running again.

It's done it for a long time and so isn't related to the new engine I've had put in. It used to do exactly the same before so it must be some issue related to something elsewhere.

When starting from cold it's completely fine.

Any ideas?

Many thanks in advance.

 

[John Jones Jr]

Can't give you a direct answer but what I would say about KE injection is check every hose, pipe including vacuum lines. Also check all electrical connections - looms getting brittle at this age. The throttle position switch & the potentiometer are often past their best at this age too.

 

[derin100]

Thanks John.
I'll check all the hoses in the morning just in case. I'm not really expecting to find any splits really as most of this stuff was renewed less than two years ago. Also, I would have hoped my mechanics would have noticed any dodgy looking hoses when they did the engine swap which was only a few weeks ago. And the car used to do this in the past before the engine swap.
I've just remembered that I haven't checked the fuses on the OVP on this car.
Might that do it?
When the idle is low (probably 500-550 rpm) it's also go a slight misfire.

Thanks again

 

[stwat]

Check the connectors and wiring to the coolant temp sender. They are known to break thus giving duff readings to the ECU. I have had to replace them on 3 of my mercs and my S had them replaced before I bought it.

 

[derin100]

Cheers! (again! )

 

[derin100]

I think I've solved it.

I remembered when it was doing this before on a couple of occasions. The first time I discovered that the spring to the right side of the throttle had become detached; the second time it had snapped completely. I'd replaced it with another spring but when I looked yesterday this spring had stretched slightly!

I've now replaced it with a more robust spring and that seems to have done the trick.

I don't know why this should work (or rather why not having or a spring that is too weak or long should cause the problem) as I don't know enough about the Jetronic system. Maybe someone more knowledgeable can explain?