I'm guessing the mixture is set too rich to compensate for a failed sensor or incorrectly set AFM plate. Too much fuel when cold will give you a rough idle, bom-bom-bom sounding exhaust and a tendency to stall with EHA connected on acceleration as current is altered to initially richen the mixture. Disconnected there is no enrichment so you have less tendency to stall than when it's connected. Just a wild guess...
Right first check the temp sensor. Do you have the values?
What is the fixed value you get at X11? It will indicate a fault code.
Don't ignore the Zero position it's a 5 second visual check and it's critical to correct mixture adjustment at idle. If zero position is out your mixture will be out at idle and it can definitely cause the stumble you speak of.
A few simple steps. Make sure your Zero position is correct (see previous posts). Lean the mixture out counter-clockwise until your basic position is at the very bottom of the vertical cylinder. Likely it won't start here. Richen it approx. 1/8th of a turn until the engine will start and hold a cold idle - this is just to get you in the ballpark. Wait till 80 deg C and you should go into closed loop mode and see fluctuating duty cycle at the pin 3 x11. Tune it by duty cycle and/or EHA current. If not and the duty cycle is fixed check the fault code it will likely pinpoint the problem.
You say the EHA current goes from 1.6-2.6ma. When is this happening? At idle, is the current moving up and down constantly or is this a one off event at some point? Can you elaborate?
87 190 E
89 190 Sport Evolution