I have been researching this topic for a while now, but I can't find anything that seems to mirror the problem I'm having.

The problem is that when I test the duty cycle on my 1991 500SL engine, the difference between the idle test and the 2000-2500 RPM test is huge. I am getting a reading of 82-90% at idle and 30-38% at 2500 RPM. I can't seem to adjust it to get it any better with the AFM adjuster or the EHA valve adjustment.

The fuel distributor has been rebuilt, the AFM potentiometer is new, the injectors are new, the O2 sensor is new, the ignition system is in good condition. The only components that I haven't tested completely are the fuel pressure regulator and the EHA valve. Neither leak and I have swapped the EHA with different ones trying to test this.

Anyway, tonight I'm going to try to buy a set of gauges to check the pressures and see what I get.

Has anyone ever seen this before? Any insight is appreciated.

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1998 E320 Wagon

1992 300D 2.5 TURBO

1991 560SEL M119.960

1986 300SDL TURBO

1992 500SL Parts Car

1991 420SEL Parts Car