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Old 12-29-2002, 02:28 PM
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Join Date: May 1999
Location: Sacramento, CA
Posts: 1,416
idle/decel microswitch

What does this part actually do? I was cleaning up my accelerator linkage a couple of days ago, and noticed that the arm on the microswitch actually rides up on top of the linkage arm and doesn't actually "click" the switch. I tried bending the arm down, but there's too much play in the joint, and it doesn't stay in contact with the side of the linkage.


1987 300E 238k mi
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Old 12-29-2002, 02:41 PM
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Join Date: Oct 2002
Location: Toronto, Canada
Posts: 700
the switch shuts off fuel flow, very good for economy, my car had the same problem, the fulcrum lever didn't reach it and it only got engaged every now and then until I replaced the spring on the lever, now it's fine.

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Old 12-30-2002, 04:38 AM
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Join Date: May 1999
Location: Sacramento, CA
Posts: 1,416
Thanks for replying. Do you know how it affects the idle control? My fuel economy isn't bad (about 24 highway, 20-21 with a 50/50 driving mix), but I do have a bit of an idle "burble" that you can feel through the chassis. (Also, rpm's will occasionally be unstable.)

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Old 12-30-2002, 08:10 AM
Join Date: Mar 2000
Location: Gainesville FL
Posts: 6,844
Good question, here is hoping for a definative answer as I don't know. The switch obviously affects decel cut-off by indentifying closed throttle, but there already was a closed throttle switch in earlier 103 KE systems and it continues after the introduction of the decel idle switch in about 88.

I can tell you it does affect idle. Its my impression that it (along with the regular throttle switch) participates in the off idle control state. This is the strategy the valve takes when the speed is "high" but the throttle is open. Normally the valve would close at "high " speed but this is not what you want to happen when idle is not the point.
Steve Brotherton
Continental Imports
Gainesville FL
Bosch Master, ASE Master, L1
33 years MB technician
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Old 12-31-2002, 04:09 PM
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Join Date: May 1999
Location: Sacramento, CA
Posts: 1,416
Alright, in that case I think I have my switches mixed up. I must be looking at the closed throttle switch in my '87.

In the case of the decel switch, it sounds like it allows the control unit to distinguish between the idle state and deceleration state (hence the name of the switch) when there is no accelerator input in both cases.

Thanks for replying. In my case this is more a question of curiosity than actual diagnosis.

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