sptt: Do a search on duty cycle adjusting and then check yours to see where you are and proceed from there. If you are outside of the design limits closed loop operation esp. idle can be affected. Mark

Thanks Saumil, I did locate it (Ignition Coil) on the right side of the fuel distributor under the Air Intake Assembly. What I'll probably do is replace both since the car is old and everything else I've replaced seems to be original equipment anyway. I'll let you know if it works! Crossing my fingers. Thanks a lot.

Steve

OK...replaced the ignition coil with the Bosh OEM replacement part. A little better idle but not a whole lot of difference. Ordered water temperature sensor, vacuum lines and connectors. If any of those don't make an improvement, I am going to just live with what I've got. Thanks for all of the help. Was hoping I could post a "solve" on that ever eluding idle issue...maybe next week?

I had a similar issue once, the culprit turned out to be a couple of cracked air hoses. When the car got hot, the cracks opened up letting air in and causing a low and rough idle.

Easy test is to spray (sparingly) carb cleaner around suspected areas. Watch for idle surges. On that motor, pay attention to the cold-start injector hose, (under intake manifold), idle air hose, and all the rubber parts that you can't see such as the boot on the bottom of the air meter. Also, the vacuum hose to the valve cover can crack and leak on the underside and look fine from above.

Also wouldn't hurt to check the idle air valve, if it's unable to change as the car warms up, that could give a similar symptom.

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-tp


1990 300SE "Corinne"- 145k daily driver - street modified differential - PARTING OUT OR SELLING SOON - PORTLAND OR. AREA - PM ME FOR DETAILS
1988 560SEL "Gunther"- 190K passes anything except a gas station
1997 S420 - 265k just bought it with a rebuilt trans. Lovely condition

Thanks TP. I sprayed the heck out of the hoses with carb cleaner but could not get a surge or change. I can try again per your areas to test but how about this? It has cooled off her in So Cal, so now, after driving on the freeway for a while and exiting to a stop, my temp gauge reads about 72-76 degrees and it idles nice. As I sit there and wait, it warms up to around 79 degress and boom! The idle drops to 500 and gets rough. I take off and go down the street, stop again, temp drops, good idle. Sit there and gets hotter...77, 78, 79 boom! Rough idle! Doesn't this sound like something is sending a false signal or something, or causing a richer run condition? Do you think this would be an air leak issue being so precise on reaction?

72-76C isn't the normal operating temp range on a M103. It's too low. If the correct 87C thermostat is installed, it may be stuck open, not allowing the motor to reach optimum operating temp. Or it's not the correct thermo. It's also possible you're getting faulty resistance readings from temp sensors. You may already know this, but the main coolant temp sensor is actually two identical sensors contained in a single assembly. One sensor sends a resistance reading to the EZL controller and the other sensor sends a reading to the CIS controller. Those signals are supposed to be identical readings, otherwise the two control units are getting conflicting information and attempting to make counteracting adjustments to the motor. It's easy to check the sensors if you have a multimeter. The temp/resistance table is listed in the FSM. There's also an air temp sensor located in the air intake cowl that can be checked and uses the same table of specs as the coolant temp sensor.

__________________
1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't

Now that sounds like what the problem might be. I have ordered that sensor and am waiting on delivery. My driving temperature is below 80 c. When I come to a stop it slowly moves up to 80 c. If it's hot out and I sit there, it will eventually get to 90 c and hold. If I take off and drive again, it will drop back down to 80 or lower depending on drive distance. I hope that is the problem and the sensor makes a difference. I certainly noticed a difference (improvement) when I replaced the O2 sensor. Thanks!

Just wanted to post back with an update. I changed out the water temp sensor in my 300E. In order to do that, I had to take off the manifold cover which was easier than I thought. Be careful if you do this and remove the water pressure if possible by taking off the radiator cap first as water sprayed all over the engine and onto my uncovered engine parts. Put everything back together and started it up until operating at normal temperature. Did not solve the problem. Then, one day, I was playing with the sensor connector and taking it on and off, on and off, while the car was idling (I was turning the connector to see if it mattered or acted differently when I connected it at a different 1,2,3,4 pattern) and since then, it has been idling fine even when temp exceeds 80 degrees and at a stop. Not sure why it's been running better, maybe the computer adjusted after running it for a while? I also replaced all of the rubber vacuum hose ends I could see and a sucking noise I used to hear down below the engine got much quieter. Anyway, so far, so good. RPM is 600 vs 500 when idling.

Hurray! After all of my parts replacements and thread reading, I have finally got my 300E with 180,000 Miles to idle nice and smooth!!! For my car the Lambda setting was misadjusted by someone else for I don't know what reason. I had been trying to adjust it with the air housing off (because I didn't have a long enough hex wrench) until I read a thread last night that said it had to be on due to the air cover temperature sensor sending signals to the computer. I did the adjustment (richer for me..clockwise) and now the thing feels like it's off when I'm in the car (well, maybe a very slight little tingle when at a stop). I hope when the warmer weather returns, it stays the same. I did wait until it reached operating temperature of 80C. And I adjusted without equipment so it might not be a perfect mixture setting. For now, I'm pumped! Thanks for everyone's help! Great forum!!!