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