My 85 500SEL idles rough (warm or cold) to the point that the car shakes noticably. This morning, I started it and noticed that there was a black soot stain on the concrete from the exhaust. I placed my hand in front of the exhaust pipe and I had small black specks all over my palm.

Any ideas?

Ray

The first thing to check for is vacuum leaks.
Mine is doing the same thing without much soot. I think I found a problem with the distributor vacuum advance not holding a vacuum. I posted yesterday about it.
I have had in the past the same problem and only had found that a vacuum hose had come loose. Hope that is all it is for you.

you might want to have the warm up regulator and fuel system pressures checked and corrected.
if they are in order look for leaky injectors.
MF

This is a new to me car and this is the first day that I have started in cold.

Lots of black soot! Engine cranks 5 or 6 times before is starts.

Once its at operating temp, it still idles a little rough but there is no noticeable black smoke.

The plug wires check out at 1275 ohms.

What else should I be checking?

No change in the idle when I spray carb cleaner around the injectors. While I was at the front of the car while it was running I heard a nasty sound that sounded like a bad bearing in a fan. It started then after a while stopped. I narrowed it down to what I think was the air pump (under the alternator). Could there be a problem with the air pump or O2 sensor that could be causing this rough idle (too rich) condition?

Ray

Where is the vacuum hose from the distributor located?

Hi Ray,
You did not say anything about looking for vacuum leaks.
You really need to do this first. It could be that simple. Vacuum leaks are usually easy to find and fix.

Could there be a problem with the air pump?
Yes the air pump has a clutch on it and only operates for a short while at startup. The clutch lining wears out and you then have metal on metal grinding sound. No you cannot replace only the clutch. Yes the air pump is expensive. What some people do is just disconnect the electric plug that controls it. That solves the grinding noise. But there is also a vacuum valve on it. The hose nipple on mine rusted and created a vacuum leak. I replaced mine and then the clutch went out.

No change in the idle when I spray carb cleaner around the injectors.
This will only expose injector seal or intake leaks that will make your car run lean not rich.

O2 sensor
I don't know. Do a search and I am sure you will find an answer.

I noticed you are new here. Welcome aboard. There is a lot of smart people here that can answer almost anything. The first thing to do is use the search engine. It works pretty good. There are a lot of questions all ready answered.

How many miles on the car?
Are you using platinum plugs?
If over 120000 has the timing chain been replaced?

Hope this helps

Thanks for the help everyone!

Gary -
I have done a search and there is a TON of things that it could be. I am trying to eliminate them one-by-one.

I replaced the plugs (not plat.) giving them a gap of .038", the ones that were in were all uniformly black with black fuzzies. I replaced the air filter, the one that was in it was very dirty and I needed to empty the filter housing of all the pine needles, sand, bugs, etc. I just put some techron cleaner and chevron premeum fuel in.

After the above (all done this morning except for the fuel) the car started with about a 1/2 crank and ran pretty good. The idle is rock steady on the tach but the car shakes a bit (maybe moter mount).

The car has 159,000 miles on it, I bought it three days ago. The car is all original every gadget works, climate control, heated front and rear seats, alarm, power front and rear seats, antenna, EVERYTHIING. The paint is like a mirror. It also came with three very big Mercedes factory service manuals in perfect condition.

The previous owner bought it at 90,000 miles and said he did nothing to the timing chain, I am making an appointment as soon as possible. He did have a new transmission installed at 100,000.

My wife, kids, and I love the car, I just want to get the bugs worked out.

Thanks,

Ray

Ray,
Sounds like you got a great car in need of a little TLC.
The soot may be nothing but needing the new plugs.
I bet you and your family enjoy the heated seats in you area.
I can only use mine a couple times a year hear in Fla.
You may want to look closer at the air pump vacuum valve. At first I did not see any problems till the nipple came off in my hand.

Robert,
The hose is on the drivers side of the distributor. I'm talking about the ignition not the fuel distributor. It is really easy to see.

I was reading your post gsmith, And was wondering if you do feel a diffrence with you idle quality and fuel consmption with your air pump workink properly. I tell you my 85 500sel is to me perfect, exept that once in a while a get alittle shake. not bad just not PERFECT. And belive me i have gone through this car up and down. But I just realized that my air pump has been diconected for a long time. I was wondering if you do feel the car to be better. in any way.

__________________
MERCEDESDOC
85 500 SEL (us car)
EIBACH SPRINGS,
16X8 LORINSER DEEP DISH
225/50/ZR16
EURO LIGHTS
SEC GRILL
WHITE GAUGES
1ST GEAR START TRANS.

Hi Raymond, My 117 engined 500SEL did the very same once but without the soot. I found a small vacuum pipe behind the RH cylinder head off. Seems this small bore pipe sends a signal to the transmission for gear shifting, fixed it back on and hey presto, problem solved !

__________________
1993 190E 2.0L (Euro.) sold
1991. 500 SEL (Euro.)
1991. 300 CE (Euro.) sold
1993. 500 E (U.S. spec.)

MERCEDESTECH
I might have given you the wrong impression about the air pump.
I did not replace the air pump. Its my understanding that it only works for a short time at startup so should not have any effect. If I had know that the clutch was bad I would of just pluged the vacuum line and not replaced the valve. My car like Ray's was new to me at the time. From the posts I seen here I am getting about the same mpg as everybody else. 14 city 17 Hwy

While I got your attention perhaps you can answer the question I posted Thurs. Should the ign vacuum advance hold a vacuum?
While checking it I got confused. It advances but does not hold a vacuum. I have never seen this before. The ones I have had go bad before would not advance at all. Like the diaphram had a hole in it not a slow leak. I cannot find/diagnose any other problems and I would hate to spend $111.00 to find out I was wrong. Still learning german engineering.

Ye it should hold vacum, if it aint I dont see how it can pull and make advance. If you put a vacum pump on it an does not hold vacum it is bad.

__________________
MERCEDESDOC
85 500 SEL (us car)
EIBACH SPRINGS,
16X8 LORINSER DEEP DISH
225/50/ZR16
EURO LIGHTS
SEC GRILL
WHITE GAUGES
1ST GEAR START TRANS.

I have been trying to track this problem down but so far haven't gotten very far.

I have noticed that on cold start there is no high idle (not sure if there is supposed to be), it starts and idles at about 600 rpm. During this time the economy gauge is a half inch off of economy. If I rev the engine to 1500 rpm or so, the economy gauge goes all the way to the economy side and the engine idles very smooth.

As soon as I notice the temp gauge moving up the car idles good and the economy gauge is all the way to the economy side.

I'm not sure if all of this is related to the black soot in the mornings or not. Can anyone offer any suggestions?

Thanks,

Ray