I'm trying to troubleshoot my 1992 190E 2.6L. Following directions from other posts, I've measured duty cycle at pins 3 and at the x11 connector.
engine not running, I get 30% initially, and 10% when actuating throttle off the stop. That's using the Mercedes definition of time at low voltage being the duty cycle. So voltage is actually high most of the time. I confirmed this using DC voltage measurements, getting 8.3 volts initially and 10.6 volts upon actuating throttle. To make sure I didn't just have leads reversed, I used chassis ground in place of pin 2 and got the same values.
I'm baffled. What could make these readings exactly opposite what they should be? The symptoms of the car are that it runs fairly normally when at mid rpm and driving, but goes rich at idle and will stumble, then clear itself when taking off from a prolonged stop.

Where should I check next? Is it possible someone made a wrong connection when working on the car? It was in a shop a long time with unsuccessful results.

You could be reading information that isn't for your later model system. I imagine that 1992 has electronic idle control for starters - I could be wrong! So check!

I recommend you get your test information from the FSM on startek first.

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1992 W201 190E 1.8 171,000 km - Daily driver
1981 W123 300D ~ 100,000 miles / 160,000 km - project car stripped to the bone
1965 Land Rover Series 2a Station Wagon CIS recovery therapy!
1961 Volvo PV544 Bare metal rat rod-ish thing

I'm here to chat about cars and to help others - I'm not here "to always be right" like an internet warrior



Don't leave that there - I'll take it to bits!

thanks, I'll check the info before going further.