The duty cycle should be fixed when cold. Once the engine is up to temp you should be able to read it.
There's a coolant temperature sensor on your engine that might have gone bad. I don't have a test procedure for it but it controls the CD start valve and other enrichment related activities. Do a search on that topic. I believe your 86 has two different coolant sensors that achieve this functionality. The links I posted make mention of it.
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