380sl 1982 - engine holds back

[blueshield11]

When I start my 380sl (1982) the first time, the engine runs fine and I can drive the car easily. When I stop the engine and start again then the engine does not run fine, holds back, makes a different sound (kind of plopping) and when putting the gaspedal down more then the engine stops running.

Fuel pump has already been replaced some time ago and the connectors of the electronics near the engine are checked.

Can somebody help me ? Any suggestions ?

[Tims450SL]

Without being an expert, I had the similar problem years back. Sounds like maybe your catalytic converter(s) are bad. When they get hot and are bad they block the exhaust flow exit. I hope you fix what is wrong!

[blueshield11]

@ Tims450sl - thanks for your reply.

There is something I need to add to the problem I mentioned above.

When I start the car the second time, it does not run smooth, but when I spray some "startpilot" into the airbox, then it runs better.
Could be a fuel problem? If so, where do I have to look ?

[BAVBMW]

This isn't going to help much, but I've got to ask, what do you mean "holds back"? We hear this from time to time from our customers, and no one seems to know what exactly it means. To us mechanics, holding back is what the engine is doing when you are coasting down a hill in gear, and the compression of the engine is slowing the vehicle, but I gather that's not what is meant by others.

As for your problem, the fact that it runs better when you manually add fuel (spray) does suggest that you might have a fuel problem. You didn't mention which injection system you have, but you could have a sticking airflow plate also. What do you have to do to get it to run good again? Wait for it to cool down? How long? How long do you have to drive before it acts up, or is it only after shutting it down and restarting?

MV

[blueshield11]

What I mean by "holding back" is something that is hard to explain for me because I am dutch. I will try to explain what I mean. When I "play" with the gaspedal then it is possible to get it on the right rpm. But when I let go the gaspedal it will go to 400/500 rpm. (I think it must be 900 rpm). When I put down the gaspedal the engine stops.
Most of the time there is white smoke coming out of the exhaust at first start.

You are also talking about cooling down, but the engine is not that warm when I do the second start and have this problem. (it takes longer here in The Netherlands to warm up the engine because the car still has the american thermostat).

So this problem occurs when the car is not even warm.

And I do not know which injection system I have. Where can I see that?

[blueshield11]

Where can I see which injection system I have ?

[ctaylor738]

An '82 380SL would have K-Jet with electronic idle speed control. If it's a US car, it would have a catalytic converter, an oxygen sensor, lambda computer, and frequency valve and some miscellaneous sensors.

So you start the car OK with a cold engine, but if you run it for a few minutes, shut it down, and then restart:

- it is hard to start
- once started, it wants to idle at 500 rpm in Park
- dies if you give it gas

Do we have the symptoms correct?

[blueshield11]

@ ctaylor738: thanks for your reply

Yes it is a US-car.
But I am sorry I do not know all the technical details about the car. Should look into it soon.

And the symptoms are almost correct.
it is NOT hard to start the second time.



I have been looking for pictures of the engine, but I cannot find any.

[ctaylor738]

I think that either your idle control unit (ICU) or one of its inputs is TU (American slang for "not working"). The ICU controls the amount of air that the idle control valve passes to the engine, which in turn controls the idle speed. The ICU has two inputs. The first is whether the transmission is in P/N or in gear. The second is if the coolant temp is below (I think 40 degrees).

The first input comes from the transmission switch. In P/N, the idle speed is supposed to be 900 cold/750 hot, in gear 650/500.

The second input comes from a temperature sensor at the back of the right cylinder head and tells the ICU whether the engine is "cold" or "hot."

The diagnostic process is to check the inputs from the temperature switch and the transmission switch, and if they are OK, replace the ICU. To check this, you need the electrical diagrams and a basic multimeter.

My guess is that your ICU is bad. The first time the car starts, it's OK. Then it fails and thinks the car is hot and in gear when in fact it's cold and in Park.

Please remember, this is my long-distance guess!

[blueshield11]

@ ctaylor738.

Thank you very much for your detailed explanation.

I will check the inputs from the temperature switch and the transmission switch.

I do have a basic multimeter. Can you tell me where I can find the electrical diagram ?

Thanks a lot.

[ctaylor738]

I would suggest that you purchase the US 107 CD from Mercedes or from any number of online vendors, or go to alldatadiy.com and get a subscription for your car. Both will give you wiring diagrams, component locations, etc. The CD has a detailed "functional" explanation of the injection and idle systems that is very useful.

This stuff may also be out on the web somewhere

[blueshield11]

I did "purchase" this evening the discription of my car at alldatadiy.com. Very helpful.

And I have already taken out the idle speed control unit from my car this afternoon.
So tonight I am going to look for "loose ends" on the print of the unit.

I will be back here when I know more.

[blueshield11]

...The print has already been "repaired" I think because there is a date on it from 2003....

I have put it back into the car this morning and I started the car and kept it running to warm up the engine. The engine sounded real fine. After 15-20 minutes the rpm decreases and the engine did not sound good. and later the engine just stopped running and no way to get it running again.
It looks like a fuel shortage. There is enough gasoline in it and it is hard for me to see why this is happening. (I am not used to having gasoline cars, for years I am driving Mercedes Diesels).

[blueshield11]

When I leave out the idle control unit from the car will the car start ? (I know I need the ICU but I want to know if the car will start without ICU.

Another question: And can the car be started without the air filter/cleaner ?

[aam]

Originally Posted by blueshield11

When I leave out the idle control unit from the car will the car start ? (I know I need the ICU but I want to know if the car will start without ICU.

Another question: And can the car be started without the air filter/cleaner ?

Ahhh. If you want help,stay on one thread, you are all over the place.
Don't give us a hard time.
Say where you are located, year, miles, on your avatar.
1. You can't start with out the idle valve or icu.
2. if you spray gas you don't spray it in the air filter box.
You spray it in the engine air intake.
3. Yes car starts with out the air box.
aam.