Tried to measure duty cycle on 90 560SEL and got very confused with the meter readings. Is it meadured at the round diagnostic connector, X11 pin 3 on this car? What kind of meter? Ive got a fluke hand held with ac and dc. I think my meter got confused, sometmes it would read 13.8 volts dc and sometimes .28 Vdc and sometimes 4vdc and always some amount of ac.

Left mix at 1/2 turn CW from where it was and about 650 rpm. 1/4 more it starts to surge, 1/2 more and the engine idles rough.

Back where I started the idle was about 950.

Any threads or articles to see?