Mercedes-Benz W126 idle speed and high idle
260 SE500 SEC560 SEL
What is the normal idle speed of the W126?
Values vary. For the M103, 650-750 rpm is given with the gear selector in N, and about 600-700 rpm when warm. In an automatic in neutral the reference value is 600-700 and in D 500-600 rpm.
Why is the W126 idle too high?
Common causes: the throttle linkage does not press the lever of the fuel cut-off switch, in which case adjusting the lever fixes it, or the sliding surfaces of the air flow sensor potentiometer are dirty. Check these first.
Is it normal for an automatic's idle to be higher in neutral than in gear?
Yes. In a Mercedes automatic the idle is slightly higher in neutral than in gear, to save fuel and the transmission. If the noise comes from the transmission, it should be investigated.
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