16-Valve idle no one can figure out

[16-Valve Kurt]

I have a US model '86 190E 16-Valve.

The card idles at at least 1300 RPM. I've taken the car two two M-B dealerships and four independent shops and no one can find the problem. The car idles at about 900-1000 RPM when cold, but as soon as the engine warms the idle shoots up. The idle is not really erratic, but it's a little hard to say before because of the impact of the AC engaging. Here is list of what has been done/checked:

-OVP relay replaced
-Idle control valve replaced
-EZL computer replaced
-O2 sensor replaced (sensor good, but no signal at sensor)
-Intake manifold removed. All boots, gaskets, hoses replaced. No techs can find a vaccum leak
-Cam timing checked
-All temp sensors checked
-Throttle plate adjustment checked
-Fuel/air mixture checked
-Engine wiring harness checked
-Valve clearance checked

After swapping out the computer, shops either indicated the harness must be bad (despite the fact that no one has found an issue with the harness, or that the already replaced EZL computer (this was actually replaced twice) or that the idle control valve must be bad).

FYI - One shop indicated cutting off the air flow to the idle control valve produces perfect idle.

I must note that my ignition switch has a problem (I had the same thing with another 190), to engage the AC and blower motor I need to turn the key back a tad. Could this have anything to do with the high idle?

Any help would be appreciated. I have spent an incredible sum of money trying to fix this problem. Everyone says they can fix it, and they can't.