M104 stumble

[benzfan]

The car is a 1996 c280. It exhibits the following symptoms;

-cold and hot starting are fine
-cold running is fine
-around town and highway running are fine
-high speed, throttle response, fuel mileage, kickdown, etc. are exhibiting no problems
-when hot, in gear only and stopped, it occasionally stumbles, like the fuel has been shut off for a fraction of a second, then restarted. It recovers to an RPM a couple hundred RPM over normal idle then quickly settles to where it belongs.
-This has gotten worse over the last while, and has not to my noticing started suddenly. In the summer, I would occasionally get a slight backfire after coasting into a corner and goosing it on the exit.
-the idle is smooth, but the tach wanders about half a needle width constantly
-occasionally when the aux. fans come on, the idle briefly drops considerably


The dealer has ruled out the OVP relay, the purge valve and the MAS by substituting new parts (no charge to me yet at all by the way)

Plugs, ends and O2 sensors were replaced 2 weeks ago as they needed work at that time. Coils are known good.

MB scan yielded only 1 fault code:
under TPM,
182 Safety fuel shut-off switch signal for HFM N3/4

The dealer now suspects the throttle actuator (ouch). Does it sound like they are on the right track? I found that if I 2-foot my driving and just rest my foot at a stop on the gas pedal, the stumble does not occur. For the weekend, I have taken a bit of the play out of the throttle by winding out the cable adjuster, and the stumble only occasionally occurs. I have not noticably increased the idle by doing this, just taken the play out until the dealer can get back under the hood Monday for some tests. My car does not have the same external idle microswitch that some of the older cars had, but what have I accomplished with the actuator by doing this? I have no intention of leaving the car like this, I just wanted to make it a touch less dangerous to drive this weekend.
TIA