Rough Idle - Bad memory theory?!

[NDavies4]

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? I haven't seen any mention of the car having such memory anywhere, but if it did then the symptoms would fit with this memory being in some way volatile.

Note, my engine type is a M104.980 which means it uses the KE-III (CIS-E) injection system with an EZL (?) ignition controller.

Any thoughts welcome.

Cheers,
Neil

[Mike Murrell]

My original reply to this thread has been removed. I had you confused with someone else. My apologies.

OK - here's a thought. You say this happens after a period of inactivity.

These systems require sufficient battery voltage to function correctly. Could it be that the battery has fallen off enough after x days to be less than efficient?

My 2 cents.

[NDavies4]

Thanks Mike,

What got me thinking along these lines was 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 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 my problem.

Any Bosch ‘Continuous Injection’ gurus out there?

Regards,
Neil