I am trying to diagnose a persistant idle problem. Is there a recommended steeing for the idle control? The Bentley manual says 1-1000 Ohms. I have overhauled a lot of the intake/fuel injection components. I think it was at 600 Ohms before, but it has no anti-tamper plug and it may have changed. I would like to have it at a conservative setting so I can try to rule it out to find the real culprit.

Thank you

The mixture pot on the AMM has a very limited range in how it affects the mixture such as you'd notice in drivability. A fine adjust.

The AMM in the LH2.0 cars is prone to changing its voltage output in chunks much too large for the mixture pot to make up for. The resistance readings mentioned in the book are no good for discriminating between good and bad AMMs unless something unusual has failed. The best way I've found to tell a good one from a bad one is by the voltage output at rest, i.e. ignition on, motor not running. A good one reads about 1.6V. I've had experience with bad (way lean) rest voltages between 1.2 and about 1.45V. The pot is a separate circuit and will not compensate for a failed AMM, but may fine adjust the mixture among "good" units.

Have you successfully used the mixture test point?
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Art Benstein near Baltimore

Art,
I am not farmiliar with the mixture test point. I would like to determine if the AMM is bad, I checked it all the ways that Bentley manual outlines, and it seemed to pass them. I am going to go pull it and check it again. I will check the Bentley for the Mixture test point as well. I could try and find a replacement in a wrecking yard to try in the car, but there aren't many Volvo's running or wrecked in Grand Forks ND!

Thank you for your time

Seth Johnson

The test point is not hard to find, it is just hard to use on LH2.0. There's a two-terminal socket coming from the harness near the AMM and ignition coil with a pink and blue/white wire. The pink one is the mixture test point; the blue/white is one you can ground to disable the idle air motor. Bentley probably tells you to use an LED tool or dwell meter. The LED tool won't work right on LH2.0 but works as advertised if you have an 85-88 LH2.2. I haven't actually tried a dwell meter, but mine is ancient and I suspect the method to be flawed because the oxygen sensor is pretty slow at idle. Probably the best way to use the test point without building an adapter is using an analog meter to watch the transitions between about zero and 3.5V. Ideal mixture is set when the meter spends equal time at both places.

I suspect yours will be stuck at one reading and not move. I also predict you won't be able to learn anything about your AMM by taking the resistance readings recommended in the Bentley-- the one they claim measures the hot wire just reads a fixed film resistor that has about zero chance of failing. Your best test is the one I suggested: Put it back in the car, peel back the boot on the AMM connector, find pin 7 (white/red) and pin 9 (orange). Turn on the ignition, measure pin 9 -- ensure you have battery voltage- around 12.5 -- engine not running. With the motor off, measure voltage at pin 7. If you have less than 1.5V, start looking for another AMM, you won't be able to compensate with the mixture adjust pot. When you find another, repeat this test. If the voltage is higher, make sure the engine coolant temp sensor is OK.
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Art Benstein near Baltimore