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Rough Idling

1K views 11 replies 5 participants last post by  Walt Williams 
#1 ·
A couple of days ago my 380SL started idling rough. I drove her to class on Wednesday and the car didn't have its usual power, ran warmer than normal, and she really drank the gas -- 1/4 tank to go 40 miles.

I have looked at the tubing that goes to the base of the injector seats and looked over the vacuum lines.

Has anyone had this happen before? Any thoughts?
 
#4 ·
For me, my rough idle and excessive fuel consumption was caused by a million things gone wrong. The list included:

1. A Bad O2 sensor
2. Misgapped resistor plugs
3. Timing out of spec
4. Bad oil and coolant sensors
5. A leaky fuel distributor.
6. A bad Warm up regulator
7. Vacuum leaks (also included in the WUR)

I'd start checking vacuum connectors on a cold engine with some carb cleaner. See if you can get the engine to increase its idle. Next, i'd check your plugs, wires, and cap.

Don't drive the car if it's consuming that much fuel. The oil in the cylinders will be washed away with gas potentially damaging the engine. Your motor oil is also probably flooded with gas as well!

Good luck.

Edit: A user on peachparts by the name of Timm9 had a similar issue with his car. Turned out the plastic air guide housing that rests beneath the air flow meter and fuel distributor had massive cracks in it that introduced a lot of unmetered air into the system.

Might be worth checking. Don't run the car in this condition!
 
#5 ·
@okyoureabeast I don't I understand what a "plastic air guide housing that rests beneath the air flow meter and fuel distributor" is. Are you referring to the rubber boot that is part of the air flow meter? I pulled the assembly just this morning and pushed and prodded on the rubber boot to see if there was any cracks. I couldn't detect any. I have done a basic inspection of the the plumbing for the idle control system. You know, the rubber tubes that attach to the injector seats. I am thinking I will have to remove the tubing in order properly inspect them. I am also looking for any cracked vacuum lines. My fear is something went wrong with the fuel distributor or WUR. I wonder is CIS will warranty their work. Iv'e been very careful to use quality gas in my car.

What would happen if the gas contained more than 10% ethanol? Maybe it could be just bad gas.

For right now I am driving my pickup -- a 54 Chevy -- until I get the problem resolved.
 
#10 · (Edited)
FOUND IT! Okay, okay. Go ahead and say it -----> "I told you so"

This a Uro part. This tube is only a year old. I will replace all the air distribution tubing with Mercedes parts. I need to wait till Friday.

I will be replacing my radiator hoses in the not too distant future -- they're also Uro.
 

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#12 ·
The basic answer is It is part of the idle control system. This system of tubes connect your idle control valve to your injector seats. When cold the idle control valve opens and allows additional air to be supplied to each injector and thus raises the idle. Your cold start valve is mounted as part of the system and injects additional gas into the tube when cold.

At least this is my understanding of how this works.
 
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