Rough warm idle on W124 - Bad Memory?

NDavies4

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I've a '92 300 CE-24 cab that is suffering from an intermittent rough idle when warm (around 80 deg). Have been down the OVP relay; leads; dizzy cap; plugs; injector cleaner;..... route - still no joy.

My problems seem to occur if I've not used the car for 3+ days, and can generally be cured if I take the car for a decent (20+ mile run). It's as if the car forgets what is an optimal warm idle and needs a bit of a run to work out the settings again.....

Does anyone know if somewhere within the engine management system the correct settings for controlling idle in a warm engine are detected and stored in some form of memory? (Note, my engine type is a M104.980 which means it uses the KE-III (CIS-E) injection system with an EZL (?) ignition controller)

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What?s got me thinking along these lines is some info I read in a Bosch Manual on 'Continuous Injection - Theory' where it discusses the workings of KE3-Jetronic systems (what's in my car I think) and KE-Motronic systems.

It talks about a thing called Adaptive Control but does seem to state that this only applies to KE-Motronic systems - on reading the text though I began wondering if such Adaptive Control was not part of my car's system, as a fault in this area would almost definitely lead to my symptoms. The text says the following:

"Adaptive control means that the control unit ?learns? to make automatic mixture adjustment. The control-unit circuitry senses nominal warm-engine cruise values. It stores those values as the normal open-loop operation, and then uses those values as a basis for both closed-loop and open-loop actuator current. The control unit continually ?relearns? the compensations necessary for changes in engine condition, or even intake air leaks.

The air-fuel ratio values are stored in the control unit?s volatile memory, so they are lost any time the battery is disconnected. If the engine runs differently after a service, even if that service was as seemingly unrelated as the installation of a radio or theft alarm, be ready to drive the car normally for about 10 minutes to re-store the nominal air-fuel mixture values in the volatile memory of the KE-Motronic control unit".


Therefore if Adaptive Control was being used in my car (even though the Manual doesn?t mention it as part of the KE3-Jetronic system), and there is a fault somewhere between my battery and the control unit?s volatile memory (that only shows itself after ?x? days of inactivity), I?d feel I might be getting somewhere towards nailing this annoying problem.

Any Bosch ?Continuous Injection? gurus out there who can advise?
 

markyce

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My 300ce was lumpy/rough on tickover when hot.
Chased it around a bit but finally threw some Redex in on the advice of my servicing guy. Solved the problem in about 2 tanks full of fuel and now not a problem.

Hope that might give you a pragmatic solution that might solve the problem at low cost
 
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NDavies4

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Thanks Mark,

Have had a go in the past with Forte 'Gas Treatment' and most recently with a fuel additive injector / fuel system cleaner called 'Red Line SI-1'.

Both seemed to make things better for a while but eventually (after 2 months or so) problem returned - though so far to a lesser degree (i.e. idle hasn't got so bad that the car would completely die on me since the 'SI-1' went in).

My understanding is that while the additives made things work better, they probably haven't got to the root cause of my problem - which I think is some component malfunction in the various bits that control the idle in a warm engine....

Through another forum I've most recently been pointed towards the Idle Control Valve (ICV) which I've duly cleaned out with carb cleaner, but problem remains.

Latest thing to get mentioned as a possible cause of a poor idle is the charcoal canister that helps deal with fuel vapours. Reading up on this at the moment.....
 

pascal

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ND,

A year ago, I had a prob with 300ce. It cut out intermitantly, but only when slowing down after say entering a roundabout without stopping first.
My local guy told me to get an injector clean additive to put in the tank. It happened only once on the first tank of fuel, and never returned while I had the car.
Just a note; maybe not related.

Pascal
 

Terminator

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I had the same problem with my 1991 300CE. Tried the fuel additives first which made little difference. Used Wynns engine oil flush at the next oil change and switched from Beru spark plugs to NGKs, which have made a big difference and the rough idling has all but disappeared. I was also using Castrol 10w 40 Magnatec which seemed to degrade very quickly and have now changed to a different brand of semi sythetic 10w 40 which retains better viscocity much longer.
 

Spike

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I had the same with Beru plugs which I got direct from the stealership. I had really bad starting and idling and an intermittent misfire just above tickover.

Switched to NGK's and all was OK.
 

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