If I hold the throttle halfway down while starting the car it does start a little easier. I'm ordering the fuel injectors soon to replace them, along with the injector seals. However, I also see parts for an injector insulator and an O-ring. Something to replace while I'm at it? Anyone with experience replacing them?

just replace the spark plugs with the new Bosch Copper-Plus models and see...I swear..start there....it's the cheapest and you do it anyway

While there was absolutely no data provided on why the plugs would improve the situation except that Japanese NGKs "NEVER" work in German cars, and that it'll just work... I swapped plugs and wires with my friend's 300E anyway. He has the H9DCOs. We both have the OEM Bosch wires, mine were somewhat newer than his.

And it solved nothing at all. Problem persisted on my car, and his car drove no differently either. It's not the plugs, or wires. Period.

I sprayed some carb cleaner around the injector seals and idle changed just a bit when I hit cylinder 4, but not that much to make me immediately think it was a leak. I'll run a couple more tests to see what else it might be. Holding the pedal halfway down while starting the car though makes it start really quickly, like 1-2 cranks, which would suggest fuel leaking into the cylinders when the car is off...

Mine has the "spluttery" idle when in gear, but it dont have the hard starting issue... hot or cold, it starts instantly.

I am going to try plugs and hope.

o2 sensor may also be part of it. My "check engine" light will illuminate after the engine has been running for 2 minutes, then it will go off 2 minutes later and dont come on again- until the next time I turn it off and start again.

Yeah, some guys just get off on these tangents without any empirical evidence to support their biases. The correct non-resistor NGK plugs work just fine in the M103 motor, as do the correct Bosch, Beru and Champion plugs.

__________________
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

you swapped your plugs with other used plugs? maybe this car is not for you....sounds like you are not liking this car....

It seems to be their 15 minutes of fame. Mark

I swapped to test your "theory." It proved wrong. My NGK plugs worked perfectly fine in the 300E. And the Bosch H9DCOs gave me the same symptoms. So, the plugs have nothing to do with it.

I like this car, but it is my beater. I don't mind spending money on it, but I'm not going to throw money away for no reason either.

Anyway, back on topic towards a resolution... Will be ordering injectors and a few misc. parts soon. Will see if it helps out the issue.

For a free test, you may want to give the EHA a small turn....I had a number of bottom end problems on my 260E that were completely resolved after I gave a 1/2 turn clockwise (rich) on the EHA. I recommend you write down exactly how far you turned and mark it so if you need to turn it back, it won't be a problem. Giving a 1/4 or 1/2 turn will raise BAR pressure in the lower fuel distributor chamber that just makes up for general wear and tear over the years throughout the system.

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2016 Monsoon Gray Audi Allroad - 21k
2008 Black Mercedes E350 4Matic Sport - 131k
2014 Jeep Wranger Unlimited Sahara - 62k
2003 Gray Mercedes ML350 - 122k

Sounds good. I think there is a "spec" to adjust it to right? 0.1mV?

one addition that made a dramatic decrease in underhood temp and the hot engine idle on my 300se /90 was the installation of a heat insulation wrap on the exhaust manifolds down to the first joints.
the temp stays at around 80 "C instead of 100C during the very hot months. A/C also is super cool due to lower temp. As the underhood temp is low at switch off the injectors should stay cleaner (lower heat soak).

mak

The last couple of times I have driven my car when I stop at a traffic light not only am I getting that little shudder, the idle is sometimes erratic. It will kinda go up and down a little. I will sometimes have to even depress the brake harder or it will roll. With this additional symptom, does this still sound like the plugs or something else? Hopefully nothing more serious.

Although it shares the same KE injection system with the 300, the 560 is a different beast entirely when it comes to idle stability. Mark

Sorry... my car is also a 300SEL. My username was from about 7 years ago.

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2004 Toyota Sequoia Limited 4wd
1991 Lincoln Town Car Executive
1991 Cadillac Sedan DeVille
1988 Mercedes 300SEL
1972 Chevrolet Caprice Kingswood Estate 9-passenger wagon
1973 Pontiac Grand Ville
(Prior MB's: 1974 240D, 1985 380SE, 1984 190D, 1993 400SEL)

Sorry I don't have an update yet guys, been working and playing with my other car lately... I have lived with the issue and it's not really bothering me enough yet. I will do the injectors though and will report back when I do to see if there are any changes.