Ralf,

I've read lots of well-meaning, but not always "on point" suggestions posted:

1.  I don't see this as a serious safety-of-flight issue, although your case seems to be more pronounced than normal.  This type of surging is common (okay, "common" might be a strong word) with all fuel-injected Lycoming engines.  They have no fuel return line, so any fuel vapor that develops has to go through the system into the engine, causing surging as each bubble passes.  The key condition is that it goes away as soon as full power is applied.  If it also goes away, as mine does, at runup power (about 1800 rpm) I would call it perfectly normal.  However, it is not normal to surge during taxi right after landing.  So, it would still be good to find the cause.

2.  The fuel system is almost totally different (refer to no. 6 below) than on a Continental engine, so most fuel system problems are different in cause and cure.  For example, there is no "low" and "high" pump speeds and if turning on the pump cures the problem (there should be no difference in fuel flow with the pump on) the problem is upstream of the servo.  You said there was no change, so the condition is caused downstream of the servo.

3.   Sorry you went to the trouble and cost to get the servo overhauled - that would be very, very unlikely to be the cause.  There is nothing in the servo that could cause this particular symptom.

4  An intake air leak in a fuel-injected engine couldn't cause this symptom - it would just increase idle speed and lean the idle mixture, and most "normal" leaks wouldn't even cause a detectible change.

5.  It looks like you have already insulated all the firewall-forward fuel lines.  The most important is the line from the servo to the distributor, but that is the one line I most often see neglected.  There is no real reason to insulate the actual injector lines - they cool off very quickly from the cooling air flow, so they won't be the cause of surging during taxi after flight.

6.  A fuel line leak that could be sucking air into the system will most likely cause surging during flight when the fuel flow is high, not during idle conditions on the ground.  So while it is remotely possible that it could be an issue, I very much doubt it.

7.  There is one element in common with the Continental fuel system and there was one previously posted suggestion that makes sense - the fuel distributor valve may be sticking open.  The round gizmo on top of the engine might look like it is merely a way to distribute the fuel to the injectors, but it is a rather delicate component with moving parts.  There is a rubber diaphragm to which fuel pressure from the servo is applied and a spring on top pushing against that pressure.  A piston is attached, and as the pressure increases the piston gradually uncovers slots in the bore.  Each slot feeds fuel to a single injector.  This valve has a purpose:  If there is any difference in injectors in length or elevation, the miniscule fuel pressure at idle could cause some injectors to get no fuel at all.  So these slots are there to equalize fuel flow during ground operations - the injector nozzle sizes have nothing to do with fuel distribution.  As the fuel flow - and pressure - increases the distributor valve opens to the point that it goes past the end of the slots so at higher power levels the fuel flows unimpeded to the nozzles.  Thus, during flight the fuel distribution is only dependent on nozzle diameters and the distributor valve has no effect.  A second function of the distributor valve is to maintain a minimum back pressure in the system upstream and the benefit of this is a reduction in fuel vaporization.  With it stuck open, there is essentially no pressure in the line from the servo to the distributor and vaporization is likely at any hot, low fuel flow condtion, exactly what you describe.  This remains true after shutdown, and with a little luck(at tight seal) a working distributor valve will reduce hot start problems.

In conclusion, it sounds like the most likely cause is a distributor valve that is stuck in the open position.  This will have no consequences at any high power condition, but will have an effect on hot idle.  It will also degrade idle fuel distribution, but depending on the injectors and injector line routing, you may not have noticed.  A fuel distributor is something you can disassemble yourself, usually without removal from the engine.  Remove the screws on top and the cover, diaphragm, spring and valve can be lifted from the assembly.  The valve should move effortlessly in the bore, and there should be no trace of dirt or contamination.  Give it a shot and let us know the result.  And you might find it useful to post the question on the Lycoming list - there are lots of Lycoming-specific experts monitoring that list.

An unrelated comment:  The vent hole on top of the distributor should be periodically inspected for signs of fuel.  Any stain should be considered serious, as it indicates a diaphragm that is leaking fuel.  If the diaphragm total ruptures fuel will spray out the vent on top of the engine and the valve could close, interrupting fuel flow to the engine.  All that could cause a power interruption during flight.  This potential problem is common to both Continental and Lycoming engines.  However, I have never heard of one failing in that mode.  Still, inspect it.

As usual, all this is just my opinion, be it ever so humble - or not :-)

Gary Casey