I have a '75 164e with the same problem, which I have not managed to correct just yet (car has been off the road for some time anyway... my username says it all... groan).

Anyway, the assembled knowledge I've seen suggests the following:

- injector seals dried out (replaced, helped a bit).
- injectors worn out/leaking down (replaced, made no difference to this problem but WOW much better fuel mileage).
- fuel pump internal check valve allowing fuel to leak back to the tank after shutoff -- the fuel rail is above the exhaust manifold... it needs the fuel in it to keep it cool after shutdown, otherwise you get vapour lock as in the old carburetor setups -- I have tried two 'good used' pumps, one would not start the car, other made no difference... recently got a NOS generic pump but have not yet installed it so I can't say if this is a cure or not.
- most esoteric fix I've heard of: there is a spot where the fuel line passes through a small bulkhead on the side of the block (I'm going from memory here)... one guy found a pinhole leak in that spot, which was just enough to cauue the problem.
- some people live with it and either install an electric fan set to run after shutdown, OR cludge a fix whereby they wire the cold start injector to a dashboard switch that allows them to give an extra shot for hot starts. I saw a number of cars with this arrangement, when I was shopping for mine.

All I can say is good luck and let me/us know if you find another cure.

With the current list price of the Djet fuel pumps, any leads on a source for a reasonably priced one would be great too :-0.

Steve
'70 142s
'75 164e
'86 740T