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Discussion Starter · #1 ·
My 91 4matic has just developed a very rough idle after it has warmed up. The engine stumbles on idle and feels like it is going to die but keeps running. Runs and performs fine other than the idle. Any thoughts?:confused:
 

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95 E320 Coupe, 11 E350 4Matic P2
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There have beena million pots about rough idling for W124's it would help you to search old posts in the future, or right off the bat I can tell you it's a quick fix as cleaning the Idle Control Valve, or change the engine harness as many do to have the car at 100%.
 

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W124 Moderator
86 190E 2.3L 16V, 2 95 320TE's, 02 S500
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I don't believe the wiring harness is an issue until you get to 92 or 93 models. As stated above, do the forum search. Tons of comments/cure's for this problem

Good Luck,

Jayare
 

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95 E320 Coupe, 11 E350 4Matic P2
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Jayare said:
I don't believe the wiring harness is an issue until you get to 92 or 93 models.

Good Luck,

Jayare
right you are I didin't payattention to the year.
 

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Mercedes E200 black. Mercedes 300ce - sold.
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761 Posts
all above are right but.......

to save the search

start with new plugs, you havnt had the engine cut out yet im guessing? (pull to a stop and she coughs and nearly dies, let off the brake and allow a little roll forward and she is ok???) (if you havnt had this yet, you will if you continue driving)

so new plugs, leads and dizzy cap also a rotar arm. (this will help the situation but its not the solution)

to be honest, id recommend a bottle of lucas injector cleaner, worked MIRACLES on my baby

if this still doesnt solve the problem you have a dodgy injector.

before you go into injector teritory, have a good look under the car whilst she is running.......

do you see any drips at all? dont just glance, keep your head down there for a few minutes. any oil or water leaks? (five bucks says you have a water problem if you see a drip)

if you see a drip, headgasket!

sorry
 

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Mercedes E200 black. Mercedes 300ce - sold.
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ooops sorry, almost forgot, if the drip is from the rad, buy a bottle of rad weld or the such and see if that makes a difference.

you wont notice a difference straight away but after a couple of days driving you should
 

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Mercedes E200 black. Mercedes 300ce - sold.
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761 Posts
sorry to butt in again but whats the start up like at cold??

does she have any rumbles or rough shakey idle at all or is she running sweet?
 

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1993 300E 3.2 AT
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im suffering from the same situation in my 93 and have replaced plugs, cleaned injectors and throtle body, replaced engine mounts (which were visibly ruined) and still have a rough idle.

Mine just lately has been stalling and the roughness no longer stops with acceleration, i even have backfiring and very slow acceleration. shes about to go under for a mass of summer projects but the harness is my next guess. not many ways to DIY out of it so a new harness may be the way to go. for your model though that doesnt seem to be a problem, as posted above check electronics, run a bottle of injector cleaner, if that helps then at least you are on the right track! best of luck,

-Zach
 

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Discussion Starter · #9 ·
This car starts cold just great. Runs smooth. When warm it starts and dies once and then starts OK. The rough idle is when warm and idling for a minute or two. I will do my normal Techron trick and see what happens. Plugs, cap,roto new. Cleaned the air mass flow entry. No leaks!!! Head gasket was done some time ago. No oil in overflow tank. No drips. I have the bottom cover off so I can see if anything is coming out. Replaced the steering box seal and that took care of all my previous mess. I'll run a tank with Techron and post the results.
 

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Mercedes E200 black. Mercedes 300ce - sold.
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dodgy injector/s
 

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Same problem here, though the slight idle stumble goes away when the engine warms up. I think. Maybe a split vacuum line that closes up with a bit of heat?

I wanted to clean the idle control valve too, but where the heck is it? is there an online manual somewhere that details this operation 'cause I couldn't find one.
 

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1991 500SL, 1993 400E, 2009 E350, 2005 SL500
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Could be a number of things. Had rough idle on my 89 300E. I changed wires and plugs, oxygen sensor, cleaned fuel injectors, changed fuel filter, replaced motor mounts, cleaned ICV and replaced OVP. Each change improved the idle till it was finally cured. That was about 15,000 miles ago. Runs so quiet at stopliights now, that sometimes it's hard to tell the engine is on.
 

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1990 300TE
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129 Posts
Oxygen sensor, people--Oxygen sensor!

Paul
 
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