'91 300SE with the 103 engine.
Well, I fought a warm start issue for 10 years, and tried virtually everything.
So I decided to tweak the EHA just to see what happens. VERY INTERESTING.

Before problems:
1. Ran like a dream, but first cold start of the day began to take two starter hits to get it going. Hit the starter a couple seconds, wouldn't fire. Stop and hit it again, fired right up every time and ran fine.

2. When the engine was warm, it started fine, unless it sat and heat-soaked for 20-30 minutes or more. Then it would fire right up on the first crank, but would go "Chug-Chug" for about 5 seconds. Then it cleared its throat and ran fine. This plagued me for at least 10 years, and slowly got worse.

So, after exhausting the fuel pressures, vacuum leak, ignition, etc; I decided to tweak the EHA and see what would happen.

I TURNED THE EHA 1/6th TURN CW.

Results:

1. The closed-loop Idle Duty cycle went rich, from 45% down to 35%, as measured with the trusty Sears voltmeter on the dianostic terminals 2&3.
This was to be expected. I left it like this for awhle, then later tweaked the air vale adjustment allen screw to bring the duty cycle back to 40-45%: no noticeable difference, see below.

2. The cold-start issue was unaffected, still takes two starter hits, and it fires up and runs fine. Hmmm, still some work to do here.

3. THE WARM START "CHUG-CHUG'' IS HEALED!
I am so thrilled! now when it heat-soaks, it seems to take a second longer to fire, but when it does, it revs momentarily and settles right down to a smooth idle.

Conclusion: tweaking the EHA per Stu Ritter's suggestion in the "Bible" seemed to work. I assume the engine now runs a bit richer when cold and in open loop after start-up, and maybe at full throttle. The richer mix at start-up seems just what I needed for the warm start.
I don't notice any difference at full throttle, which rarely gets used anyway.

I'm still going to play a bit with the cold start issue to see if I can get it to jump off on first try. the cold start injector will be my next target.

No more Chug-chug, no more chug-chug. Life is good!

DG