Can anyone out there help with this?
Car is '95 164 LS 24V with Motronic1.7 EMS.
Symptoms are idling at between 1500-2000RPM, surging, abrupt over-run cutoff, plugs getting sooty, sub 20mpg (gulp!), error code 1223 (lamda probe regulation faulty). I suspect the lamda probe problem may be more symptom than cause, which appears from above to be an over-rich mixture. It's like this most of the time, but sometimes idle drops back to about 1100 RPM (quite smoothly) or, (rarely) to about 800, where it is a little rougher sounding than it should be.
I've changed the plugs and cleaned all connectors under the bonnet (at least, all I can find). It ran better for a while when I changed the plugs, but it's gone back to how it was so the new ones are obviously getting fouled. The warning light only came on after I cleaned the connectors.
I checked for air leaks by spraying WD40 around all junctions and listening for change in engine note. The air filter looks fine - it's only 15 months old.
I assume it's something to do with air flow meter or possibly cam angle sensor. I did notice when I changed the plugs that the intake plenum was quite mucky inside.
Any ideas, anyone?