I found what might be a $3.00 improvement to the somewhat rough idle these cars suffer. On my 1988 300ce the idle control valve connector had lost part of the plastic or rubber, whatever it is made of, and I bought a new one. When I removed the old connector and took out the wires I noticed a gap or separation in the metal plugs at the ends of the wires, causing a loose fit. I tightened each plug with pliers, cleaned the black greasy stuff out of the plugs and off the icv prongs, and reinstalled. The idle was noticeably smooother, although still not perfect. The part number for the new connector, which mb calls a pin bushing, is 011-545-71-28. Hope this helps.

When my car is at rest and in gear, the idle roughens when there appears to be a slight increase in rpms and oil pressure. Any other connectors that might be checked to smooth out the idle?

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)

Are you able to post a pic by any chance?

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

sorry, no, don't have a digital camera. What image would you like to see?

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)

Where is the idle control valve connector located?

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1989 300CE Astralsilber/Schwarz
1992 300CE Schwarz/Schwarz

Theoretically an inline six should idle butter smooth, the the requirement to maintain a stoichiometric mixture at idle for proper operation of the emission control system causes some slight idle roughness that cannot be cured.

MB service literature states that lambda equipped 103s will not idle as smoothly as non lambda verisons that run a richer idle mixture. Best idle is usually achieved at at A/F ratio of about 12.5:1, which is 20 percent richer than stoich.

Duke

Duke:
what would be the best mixture setting ( duty cycle and EHA current) for a W126(560SEL) for best idling and best cold start( shortest time to crank and engine started..) and still pass california smog?

thx,
emmy

The mechanical components of the KE system and the mixture adjustment provide a "base mixture" that the lambda system continuously corrects once the system goes into closed loop operation, so you cannot "adjust" the warmed up idle mixture because the lambda system will always correct it to stoichiometric as long as the initial adjustment is not so far off that it exceeds the lambda system's control authority. The "E" portion of the KE system also provide cranking and warmup richness ABOVE the base mechanical mixture adjustment.

The base mixture is adjusted by observing the "duty cycle" that has been discussed to great extent. MB service literature says the average observed duty cycle at idle should be withing 10 percent of the average duty cycle observed at 2500, and since a duty cycle of less that 50 percent indicates a slightly rich basic mixture, this is what you should shoot for.

On my car the average "eyeball" duty cycle is about 45 percent at idle and 55 percent at 2500, and I consider this to be ideal, and BTW, I have NEVER adjusted it. That's just where is was the first time I measured it about a year ago and I left well enough alone. A slighly rich mixture should aid "cold starts" and my car cold starts instantly, even after sitting for a week or two, because I don't drive it that often.

Another consideration is that the EPA certification test "cold start" is at about 70F, and I have always observed that my car cold starts a little better at, say 40-50 degrees, than room temperature. Since the EPA cold start is at room temperature, cars often exhibit the worst cold starting in this temp range because they set them on the ragged edge of leaness for good cold starts at room temp. About 80 percent of the TOTAL emissions for this 45 minute test occur in the first couple of minutes, which is why they want as lean a mixture as possible at a room temp. cold start.

You all should notice that the "cold idle" below 60C coolant temperature is smoother than at operating temperature. This is because 60C is about the point that the lambda system comes on line and corrects the mixture to stoich. If your duty cycle is a little under 50 percent at idle it is richer prior to going into closed loop, and it will idle smoother.

At about 60C when the system goes into closed loop and maintains a stoich. idle mixture is when you begin to pickup that characteristic idle roughness, but I think it's more prevalent on the inline sixes than the V-8s. Also, anecdotal evidence from a friend with a 560SEL and V-8 owners on this forum indicate that the V-8s don't have as big an "emission problem" as the sixes.

If you need some "assistance" passing CA or any other state's emission tests, visit the following thread and the link in this thread to a second thread.

http://www.peachparts.com/shopforum/tech-help/117048-successful-ca-asm-emission-test-ke-fuel-system.html#post833484

"Adjusting" the mixture via the duty cycle reading will NOT effect emission test results as long as it is not so far off that the lambda system cannot make the correction to stoich. Many KE-equipped engines are on the ragged edge of the emission limits or have marginal failures even though everything is basically in proper working order. Catalyst aging is probably the primary culprit, and this is why you must ensure that your car is properly "conditioned", which requires you to "manage" your test as I outlined in the referenced threads.

Beyond this, there are some options to alter the ignition timing map, which can turn a marginal failure into a pass or provide a comfortable passing margin.

Duke

Duke, my 1988 300ce just passed the NY emissions. My one question involves NOx- my reading was a negative .02. What does that signify? Thanks.

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)

Duke:
thx for the explanation. I am at about 52% idle and 57% 2500RPM. I know I am on the lean side. My cold start is within 5 sec of cranking, but seems could be better because I remember it used to be able to start right-up within a second. I have done quite a few things already to make sure everything else are working properly...things that I have learned via the forum and lots of readings, and have resolved quite a few things...rough idle, high idle to name a few.....I will try and adjust the mixture a bit more to the rich side....

thx,
emmy

Your test report should state the units of measure, however, a "negative" number is perplexing.

Emissions are usually measured in either PPM (parts per million) or percent. One PPM equals .0001 percent, so the unit of measure is usually chosen based on the sensitivity of the measuring equipment and to minimize the number of zeros relative to the significant digits so the data is easy to read. If your car is tested using the I/M 240 procedure the emissions are usually measured in grams per mile.

In California HC and NOx emissions are reported in PPM and CO and O2 are reported in percent; O2 is not an emission, but it's a very useful diagnostic tool to determine how well the emission control system is functioning.

A NOx reading of .02 percent is the same as 200 PPM using the above stated conversion, however, a negative number doesn't make any sense. Could it be that the "-" is a dash as opposed to an algebraic sign?

Duke

You're base mixture is a little lean at both idle and 2500 and is well within ten percent, so you have the option of richening it, and this should not effect measured emissions. If you richen the base mixture to the range of 40-45 percent duty cycle at idle, you will probably experience quicker colds starts, and the duty cycle deviation between idle and 2500 should still be within the 10 percent spec.

I reviewed my data and my idle duty cycle reading was in the range of 40-45 percent (It should move around a bit as you observe the meter) at idle and 50-55 percent at 2500, so the "averages" are actually about 42.5/52.5, which puts it right at the spec limit, but since my cold starts are excellent and emissions are okay, I left it alone.

Duke