I don't want to answer for others but there's a coax cable for the crankshaft position sensor that runs to the electronic ignition unit. There's a spec for the resistance of that in the FSM
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The EZL switchable timing resistor sits near to the electronic ignition unit if fitted. Otherwise a resistor lives nearer to the fuel injectors (from the pictures I've seen). Note there can be two of these switchable resistors. There's one for the electronic ignition and one for the ECU. As far as I know the one at the ECU shouldn't be messed with - it has an anti-tamper wire fixing it.
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A high idle of about 1200 to 1500 rpm is meant to indicate an inoperable air idle control valve.
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To measure Duty cycle there are tips here
BOSCH KE3-JETRONIC MIXTURE ADJUSTMENT
If you don't have a handy Duty cycle button on your multimeter.
The "Duty cycle error codes" are not the same for all vehicle types - make sure you look in the correct section of the FSM to find out what they mean.
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I also think the DIY addition of the resistor didn't make a great enough change. If you look in the FSM for the effect of changing the coolant temperature into fooling the ECU to stay in a warm up phase (for example) you need kilo ohms and kilo ohms to do this. A few ohms probably hasn't made much of a difference. (Unless it has been wired in some way I don't understand!)