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Old 12-04-2010, 05:21 PM
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Join Date: Dec 2010
Location: Austin, TX and LU, CH
Posts: 58
1992 300e (USA) Warm Start, Rich Idle Issues

Car had been sitting for a couple years. I replaced the brittle rubber breather tube (valve cover to air filter) and fixed all the broken smaller vacuum lines and replaced the battery. I then flushed the tank, replaced the in tank screen, both pumps, and flushed the remaining bad gas from the filter and lines. Labeled and removed the injectors and cleaned them on my bench and flowed them; Three at about 50ml three at about 60ml. Removed fuel distributor, installed injectors, put plastic bottles over injectors and checked flow with distributor plunger pushed completely in (WOT). Adjusted flow rates of four injectors until all injectors flowed the same. Cleaned the throttle body and removed the bad gas that had puddled under the butterfly, check the EGR valve and blew air through the EGR tube. Put it all back together after more cleaning and it started right up. Great idle until warm and then idle hunted until the motor died. Would only start (warm) with acc pedal on the floor.

Assuming a vacuum leak, I replaced both hoses to the Idle Speed Air Valve (Y6) (please correct me if it has another name. It sits right above the #2 intake runner.) since they were hard. Started right up again (cold), but idle hunted again when warm. Checked X11 (driverís fender) at 2 and 3. Key On, Engine OFF
8.63 volts / 12.56 volts at battery
With Engine running I always get about 12.4 volts until I rev the motor, then I get about 7 volts (fluctuating)
Checked 16 pin connector right in front of battery at pin three. Took pin three to ground for about three seconds and got one flash. Checked OVP relay fuse, good.
Installed wide band O2 sensor in the tailpipe and saw 9 / 1 at idle. Played with Idle Control setting (3 mm Allen) until response was good and wide band told me I was in the 13 / 1 area (at no load). Interestingly I found that going slightly richer on the idle setting solved my hunting idle problem. Let car idle again and I was back to 9 / 1. Turned car off and tried to restart. Once again, only starts with throttle fully open. Once running again, I disconnected the O2 sensor. Idle stumbled, so I reconnected it and idle returned to normal.

Checked X11 at 2 and 3 again. Same fixed high voltage until I rev the motor. About all I have left to check is the current to the Electrohydraulic Actuator, but have not because I would have to make a piggyback harness.
Is the CIS-E system supposed to run at 9 / 1 at idle?
Isnít the Key On Engine Off X11 2-3 reading supposed to be closer to 3.8 volts?

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Old 12-04-2010, 07:07 PM
sptt's Avatar
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Join Date: Sep 2009
Location: Orange County, California
Posts: 691
Since you have done all that, I would also replace the EHA valve. Shop on Ebay and you should be able to get from one place that sells them for 217.00. Solved all of my start, cold and warm idle issues. After install, I had to readjust air/fuel mixture about 3/4 clockwise in my car but now it is perfect. Also, if you haven't gotten new plugs, get the copper non-resistor (usually cheap) style...this car runs better with these plugs vs. the new fancy ones. I learned from experience.
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Old 12-06-2010, 06:56 PM
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Join Date: Dec 2010
Location: Austin, TX and LU, CH
Posts: 58
The EHA is adjustable. Mine ohmed at about 20, so I played with the adjustment to see if I could get rid of my rich idle. What I thought was odd was that leaning out the EHA adjustment leaned out the entire rev range. When I used the idle adjust screw to get the mixture correct at higher revs, I was right back to 9 to 1. I did test the O2 sensor and found it bad. When I reinstalled I got a no TD signal voltage at #3 of X11. I pulled the MAS box and the control unit to check continuity and found that the pin I needed on the control unit did not exist. I plugged it all back together and now I don’t have fuel pressure. I removed the MAS control unit and plugged it back in, still no fuel. Pulled the O2 and EHA leads to go to open loop and still no fuel.

The fuel pump relay is built into the MAS control unit, correct? Any way to test the unit out of the car?

I also found the IAT sensor was bad (open circuit), so it was replaced prior to all the above. I guess that was the reason for the high voltage at #3 of X11 right off the bat, though it didn’t really match up at 80%. Will two faults add up at #3, or will it just give the highest faults first?

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