Lumpy Idle 380SL - The Saga Continues

[ctaylor738]

From the day my 380SL arrived in my driveway (on a flatbed), it has had a rich and lumpy idle. Until last night, when HBofinger came over and re-soldered the idle control unit, it also had a surging, rich, and lumpy idle.

It does not seem to be a specific cylinder. I "cracked" three injector lines (one at a time) on the FD, with barely a change in idle. I also disconnected a couple of plug wires with not much change.

There were small bubbles in the gas that came out of the FD.

The spark was very strong.

Pulled a plug and it was very sooty.

Leaning the mixture made the idle worse.

On/off ratio fluctuating around 52-53%

In the last 6 months:

FD, injectors/seals, idle valve, all air hoses replaced. Idle control unit re-soldered. Intake manifold resealed.

Fuel flow and pressures (system and working) were checked about three months ago, and were very close to spec. Starting and running otherwise good.

This is a euro engine (compression and cams) with the US injection and controls.

Makes no sense!