Your readings look fine up until you go into closed loop operation. What does that 92% reading go to when you rev to 2500rpm+? The EHA does not affect idle duty cycle at all. The fact that its going into closed loop means that the engine ECU is good. Otherwise....massive vacuum leak, coolant temp sensor, potentiometer, throttle body WOT switch. Whats the history on the O2 sensor?

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http://i193.photobucket.com/albums/z...-RESIZED-1.jpg
1991 300E - 212K and rising fast...

Hello,

As of now the engine fluctuated between 45 and 60% when in closed loop and idling in PARK gear.

When I rev to 2500 RPM and hole the RPMS at 2500, I saw that the duty cycle began to drop in value of about 3% every second until the multimeter read 0.00%.

The O2 sensor was replaced in April of this year with a new unit.

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2006 BMW M5 "Heidi" @ 109,000 miles
2005 MBZ C55 AMG "Lorelai" @ 165,000 miles
1991 MBZ 300E "Benzachino II" @ 165,000 miles
1990 MBZ 500SL "Shoshanna" @ 118,000 miles

(On the hunt for a good used M103 engine as of 6/10/23, PM me if you have one to sell!)