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Old 11-13-2001, 03:36 PM
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Join Date: Mar 2001
Location: SF
Posts: 201
Unhappy Volume air flow sensor position sensor-86 300E

Hey folks, I got a 40% duty cycle fault on my 86 300E- 5 spd yesterday. I have had Hi idle, warm and cold @1400rpm since I got the car. My book says it a "Volume air flow sensor position indicator" fault-either between the CFI module or the sensor its self is bad. The question is 1) Has anyone ever had this fault? 2) The MB manual also usues the term Air flow sensor potentiameter (I know, same thing) but claims you need a Contact box . Does anyone know the proper way to test it? Volt/Ohm values? Thanks again. PS Is it true that once this is fixed, another fault with a higher duty cycle can be next?
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Old 11-13-2001, 04:10 PM
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I've seen alot of airflow meters bite the big one!
Test it with an ohmmeter as follows, center pin is common,measure between common and pin one while slowly depressing air sensor plate,the reading should change throughout the movement of the sensor with no major open circuits(threr is usually one halfway down)
Next measure common to pin three and look for the same results.
I don't remember airflow meters causing high idle like you describe.
The answer to the last question;yes you may have other codes as well!
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Old 11-13-2001, 04:30 PM
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Join Date: Jun 1999
Posts: 74

Can you explain the circuit used for retrevial of the codes. I would like to build one.

89 300SEL
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Old 11-13-2001, 05:08 PM
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blink code tool

Look for post dated 11/12/01 as self made blink code tool.
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Old 11-13-2001, 05:29 PM
Join Date: Mar 1999
Location: Tucker, Ga USA
Posts: 12,153
Only 1988(California) & later cars have this blink code system for the fuel system!
Won't help on a 1986 car! Duty cycle is the only way to diagnose faults on this car.
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