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Old 12-09-2010, 02:28 PM
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Join Date: Oct 2006
Location: Indian Waters, Florida
Posts: 136
High idle. 1991 420 SEL

I know this has been done to death but, with my limited electronical knowledge Iím stuck.
Trying to run down a high idle. Recently re-did the intake manifold. All the soft bits and vacuum hoses and ends. Replaced the throttle valve switch because you canít get to it without removing the intake again. New injectors, holders, O-Rings. Cleaned the ICV.
Engine had been running rough and surging. This fixed that problem but, now I have high idle. About 1100 rpm.
Checking my lamda on/off ratio with a Fluke O-scope per landiss.com/mixture.htm procedure. 49 state 70% type.
What Iíve found.
Static Test:
1. Switch on: 70% duty cycle
2. Partial depress Air Flow Sensor plate: 40% duty cycle. Should be 10%
3. Fully depress Air Flow Sensor plate: 70% duty cycle. Should be 20%.
When Air Flow Sensor plate returns to full closed: 40% duty cycle. Should go back to 70%?
Step 2. Says to check Throttle Valve Switch. Job 07.3-121. Brand new.
Step 3. Says to check Air Flow Sensor Potentiometer. Job 07.3-121.
Question. How do you check this 3 pin connector?
Have a copy of Job 07.3-121 but I donít read Greek.
Could some electrical type please explain this in Neanderthal terms?

Thanks, Dave

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