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Old 08-03-2002, 12:42 AM
mbe32094's Avatar
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Join Date: Feb 2002
Location: Bay area, CA
Posts: 107
Thumbs up Erratic Idle on '94 E320 Solved!!!

Erratic idling gone. My car was idling badly when it was in park position from 550 and jumping to 1200 rpm. Also, when decelerating I can also feel the erratic idling. I have no problem whatsoever when I accelerate. This causes my smog inspection to fail in idle rpm mode. When I checked the reading on my diagnostic box, The led gives off 10 flashes that tells me the mass air flow sensor is bad. To make sure that the air flow sensor was the one that really causing the problem, I disassembled the EGR pipe and cleaned the carbon deposits inside. I also cleaned the trotle valve and the intake manifold pipe and poured injector cleaner in the gas tank. Everything else failed so, I suspect that the air flow sensor was really the problem. I took out the old sensor and measured its resistance values on different terminals as my reference. These are my readings (bad sensor) terminals 1-4 = 245K ohms, 4-5=10 ohms, 1-2 = 247K, 2-4 = 1.53K. The voltage reading on the connector wires: 2-4, 2-1, 2-5 all are 14.7V. New sensor readings (good one) 1-4=25K, 4-5=43.6K, 1-2=25.9K, 2-4=789 ohms. Anyone who has a problem like mine you can refer to these values before you commit yourself of a new sensor. I bought mine here and I got it the next day.
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Old 08-03-2002, 01:04 PM
engatwork's Avatar
Join Date: May 2000
Location: Soperton, Ga. USA
Posts: 11,235
1995 E320, readings are 1-4 260k ohm, 4-5 11 ohm, 1-2 260k ohm and 2-4 1.8k ohms. I am not getting any codes nor check engine light but there is a very, very slight miss at idle and the gas milage is only around 24 mph city/hwy combined.
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Old 08-03-2002, 02:49 PM
mbe32094's Avatar
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Join Date: Feb 2002
Location: Bay area, CA
Posts: 107
If it's only a slight miss at idle then probably the check engine light did not sense the problem yet till you get an erratic idle just like mine. I didn't get either when the problem was still minimal. You may take it as a reference only. The difference in values may differ from what you got but I give it a plus or minus 5%.
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Old 08-03-2002, 05:38 PM
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Join Date: Aug 1999
Location: Florida / N.H.
Posts: 8,768
The readings may have some reference value and show open circuits, but the resistance of these units is a comparison circuit
[ measured internally w/wheatstone bridge]where the resistance is continuingly changing, and they also has a heater circuit that changes the R value of one side of the comparision.
Resistance measurement also gives meter power to the heater
on certain pins. [ changing the measured resistance]. You will also notice that resistance is polarity sensitive [ meaning you get 2 different readings from same pins if you reverse lead polarity..
So , I guess [ and someone here knows for sure] that the only way to actually tell is to monitor the output voltage/wave form to the ECU from the unit...

I would be curious to see what readings you get from the old and new with polarity in mind and the same meter..
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Old 08-05-2002, 01:30 AM
mbe32094's Avatar
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Join Date: Feb 2002
Location: Bay area, CA
Posts: 107
I don't have a sophisticated equipment to do all these types of measurements.I used a digital multimeter for measurements. What I did was I disconnected the old sensor and measured the resistance values between two terminals and compared those readings with the new sensor. Even if I reversed the leads of the meter the results are still the same. I don't have a schematic diagram and the theory and operation of the sensor so I cannot tell what really the function of each component and how they behave in the circuit.
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