Rough idle when cold - Mercedes-Benz Forum
 
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post #1 of 7 (permalink) Old 06-11-2019, 09:56 AM Thread Starter
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Date registered: Apr 2019
Vehicle: 1992 300SE
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Rough idle when cold

Looking for Advice, 1992 300SE,

The issue is rough idle, it used to be worse but after replacing spark plugs and cleaning MAF runs a little better, however when the car is cold, it starts fine but the RPM drop to almost stalling and then rev up to about 2K, this keeps happening for a few minutes. After the car warms up the idle is Okay but not prefect, still feels a little rough.

Thank in advance for your input
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post #2 of 7 (permalink) Old 06-11-2019, 12:56 PM
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Brittle breather hoses, distributor cap would be worth looking at


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post #3 of 7 (permalink) Old 07-08-2019, 09:23 AM Thread Starter
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Update: Changed the distributor cap and rotor, replaced a breather hose. Idle is better, however on start the RPMs are still unstable, the car almost stalls then RPMs increase after 30 seconds engine stabilizes. Once warmed up all good. Looking for advice. Thank you
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post #4 of 7 (permalink) Old 07-08-2019, 09:40 PM
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Originally Posted by Gene Reyzin View Post
Update: Changed the distributor cap and rotor, replaced a breather hose. Idle is better, however on start the RPMs are still unstable, the car almost stalls then RPMs increase after 30 seconds engine stabilizes. Once warmed up all good. Looking for advice. Thank you

I'm having a similar with the idle. I've been chasing this thing for 6 months. It has (tremors) after some spirted driving or long road trips. I have changed:

fuel injectors

fuel pressure regulator

fuel filter

fuel pumps were done less then 10k ago

plugs

still have the same problem. I was told today at a shop that my friends swears by that I probably need coils. I'll up date you when I do unless someone here has another suggestion?
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post #5 of 7 (permalink) Old 07-09-2019, 08:58 AM
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Any one try the fuel pressure regulator? That solved one of my problems.
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post #6 of 7 (permalink) Old 07-10-2019, 02:07 PM
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It could be the ignition control module maybe. I had a similar problem, car would drop way down in rpms at stoplights and seem like it wanted to die for a sec.
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post #7 of 7 (permalink) Old Today, 12:03 PM Thread Starter
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Got a OBD code reader and this what I came up with:

Socket 7 Code 2 3 and 5

2 - Cruise control/idle speed control module

3 - Cruise control/speed control actuator

5 - and stop lamp switch

I am thinking this where the problem lies.

Any suggestions?
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