W124 Lumpy Tickover Fixed

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Sp!ke

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After scratching my head for a few weeks trying to get to the bottom of my problem, I stumbled accross the cause today almost by accident. Its funny how sometimes you just overlook the easy things.

I was having a poke around the throttle linkage and noticed the absense of a spring. On examination, I noticed the if a spring was fitted then when the throttle was released it activated a little switch (circled). I attached an elastic band in place of the missing spring and all of a sudden my tickover is stable. I dont know what the switch is or does but 'd be interested to find out.
 

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Its the Idle Micro Switch. To set up the tickover the bar must be sat against the switch, depressing it. Turn the nut on the accelorator end of the cable to adjust the tickover (its in the drivers footwell)
 
Well then, that was a cheap fix. :)

What does the switch actually control? It only seems to be a simple on/off rather than having any kind of adjustment.
 
I think the switch controls the amount of fuel into the system while ticking over. A sort of restrictor. Someone may be better versed in this than I. Hope so :D
 
Spike is the fuel injection or carburettor fed?

The switch will do different things in either case, but in essence the engine requires a richer mixture when idleing than under cruise conditions.
The throttle flap being slightly open was keeping the fuel mixture set to cruise either by not drawing fuel via the idle port in the case of a carburettor, or by not switching the fuel mixture to idle in the case of injected setup.
 
Its injected. The switch is only activated when the throttle is completely released.

Bought the spring today since the dealership had stock. Nice to have my tickover regular again for £180 :)
 
Sp!ke said:
Its injected. The switch is only activated when the throttle is completely released.

Bought the spring today since the dealership had stock. Nice to have my tickover regular again for £180 :)


£180 for a spring, what is is made of titanium encrusted with diamonds??

Or did you mean £1.80? ;)
 
I have the same rough idle with my 1997 E300TD. Do you think it could be the same problem?

Cheers
 

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