Duty Cycle 0.0%
 

I've been trying to fix a low idle problem on my '93 190E 2.3. The Idle Control Valve operates (clicks) when I turn the key on and it releases after 10 seconds. I checked the amperage at the ICV when I turn the key on and it reads 1.3a, after 10 seconds, zero amps. I checked the amperage with the engine running and it reads zero amps, should be 580ma, +/- 50ma. The ICV is doing nothing with the engine running, I can unplug it and no change. It stays in the rest position with a slight opening, and the resistance across pins 1 & 2 is 9 ohms. Also, the ICV vacuum hoses are new.

With the key on engine off, the EHA reads 20ma, and 20 ohms. When I start the engine, the EHA current drops to 3.4 to 4ma. If I unplug the O2 sensor, the EHA current drops to .01 to .02ma.

With the engine running at operating temperature and the O2 sensor unplugged, the duty cycle reads 0.0%, and 12.6 volts. If I put a D cell battery on the Sensor control lead, the EHA current rises, but the duty cycle still reads 0.0%. If I put ground on the O2 sensor control lead the EHA current goes negative and the duty cycle remains at 0.00 %.

I had to adjust the idle mixture control by ear to obtain decent idle and rpms. The engine runs good, decent mpg's, excellent cold and warm starts, but the idle is not like it used to be. When I start the engine cold, I do not get the Cold running enrichment, it starts at 6-700 rpms and climbs to 1100 rpms. Put the car in D and the rpms drop to 750, then with the A/C on it drops to 550 to 600. It used to maintain the 700 to 750 rpms.

No current at the Idle Control Valve with the engine running is a concern, along with 0.00% duty cycle and battery voltage between pins 2 & 3 at the diagnostic port.

I'm using the Sears 82139 VOM with the duty cycle feature and the button pushed to read %.

Any thoughts?

Late KE systems have to be put into the diagnostic mode in order to read duty cycle. It takes grounding the diagnostic socket on the passenger side.

Thanks Steve, are you referring to grounding pin #3 for 2 to 4 seconds that I read in your Electronic Engine Controls article? If so, how do I take it out of diagnostic mode when finished?

Thanks,

Dave

Turn the ignition off.

Is this also required on early California models, say an '89 300E?

The 02 sensor must NOT be unplugged to read duty cycle.

Try it again with the o2 sensor plugged in and working with the engine at operating temperature.
Acky

Also, in order to take a voltage reading from the O2 sensor, do you have to unplug the single wire connector below the passenger floor mat and attach the red lead of the dmm to the green wire side?