Diesel Injector Pump...

I have a 1990 Mercedes 350 SDT Model 3B35 with a 603 6cyl. with 180K miles...
When started cold, the engine does not go to high idle. Once it warms up it runs fine but, when cold it smokes a bit and lopes. I am told
there is a sensor that activates the Injector pump to enrich the fuel until warm. I have heard that there is a sensor either in the goose neck of the water pump (Not either of those, one is fan and the other temp guage), on the radiator, or in the windshield washer fluid resevoir. How can I test to see if it is a sensor or the injector pump? If I want to try to test the pump can I apply voltage to the activator on the pump? Any help from your experienced group would be of reat help. The locals won't touch a Mercedes..!
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