My M103 has just 60K miles and I wish it would idle smoother. New injectors, cap, rotor, wires, correct plugs and 02 sensor. Almost there....

I actually replaced the Air Temp Sensor as someone suggested and it improved my idle and stalling today in these hot temps. Then I went and bought Bosch +2 Irridium Plugs ($32.00) and it got even better. It still doesn't want to start though. Must be my fuel accumulator losing the pressure build up to the fuel distributor.

Anything new on the idle?

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Peach Parts W124.128 User Group.

80 280SL
85 300SD
87 300TD
92 300D 2.5 Turbo
92 300TE 4Matic

My idle is not perfect but good enough, not much more I can do about it, 9 on a scale of 10 of smoothness. Car runs super so I've come to accept it.

Interesting that this thread has been resurrected.

I'll take my shot at solving the problem...since I've had a rough idle in my 500SL for over three years now. In that time the engine has been torn completely down and rebuilt. The problem still exists at low idle. Increase the RPM and it's smooth as silk. Tech manual says the idle on mine should be 650rpm +100 or -50. So, from 600-750rpm. Mine sits at 500rpm. Adjusting the mixture on the fuel distributor doesn't make the problem go away. Nor does increasing the idle by manually adjusting the linkage. The electronics bring the idle right back to 500rpm.

My mechanic has told me that the problem is in the throttle valve. Looking at my engine (117.962) manual, I'll guess a weak spring (part # 117 993 03 10). Or it could just be an adjustment to the butterfly plate. Getting to the throttle valve is a bear.

The throttle valve sits at the front of the engine and down low. The throat of the black boot (air flow housing) that bolts to the the bottom of the air flow sensor, clamps to the throttle valve housing. In order to get there, you have to remove the fuel distributor and air flow sensor. Notihing particularly hard about doing that, but it is time consuming.

What the adjustment will be is beyond me. I don't know if there is a screw type adjustment that you can make with an electronic meter or not. However, this is too big a job to tie into just on the hope you can figure it out once there.

Sometime in the next month or so I plan to tear into it and sic my mechanic on the fix.

Don

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Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000

My '91 300E idles now as perfect as I would expect it to when it was new. However, it got progressively better as I replaced parts and not just from one or two parts. Biggest improvements came from ICV Hoses which had cracks in them and were hard as plastic (biggest idle improvement), replacing O2 Sensor (stopped the hunting idle), fuel injectors (better acceleration), and EHA Valve (which, I'm not sure was bad in the first place but could have been previously messed with and is very expensive for the size of the part). I also replaced all of the vacuum lines which was very easy. OVP did nothing. Needless to say I had tried new plug wires, coil, and plugs first with little noticeable difference at the time. I have 211K on it now and bought with 170K. Next thing is the cap to help the cold start, two cranker. When I start it now, it immediately idles at about 800-1000 rpm then drops down to about 600-700 rpm when warm.

I also replaced all the hoses and fittings during the rebuild, but not the O2 sensor--though it was replaced a while before I started the rebuild of the engine.. Might be worth the few bucks to give it a shot.

Tnx,

Don

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Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000

O2 wasn't that hard to do. I bought a similar one ('05 Mustang Bosch) and spliced it in.

I know where it is and how to do it. Will take a shot at it this week. Thanks.

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Don
'85 500SL (Euro) - 186,000 w/a complete restoration and engine rebuild at 154,000
'95 C280 - 174,000