Engine runs rough/stalls during startup/warmup
 

I have read several threads out there on these or similar symptoms. Just want to make sure I will be looking in the right place when I start trying to fix this.

1984 190E 4 Cylinder 1.9 liter

When I start the car up, RPM's run really really low (between 500 and 700). If the RPM's drop below 500, the car usually stalls. If I push the gas, the car sputters, lags behind the gas pedal and just runs poorly. Eventually, If I can get the RPM's above 2,000 things level off and the engine runs smoothly. If It drops below that level it starts sputtering and acting strange again. Eventually, after running for a while at 2,000 RPM, the car runs well enough to drive without stalling. A few things I have noticed. These symptons are worse on hot days after the car has been sitting in the sun for long periods of time (I.E., sympoms often do not show themselves when I start it up in the morning to go to work however when i leave work, the car has these problems). Onces the car gets up to speed, everything runs fine.

Research indicates this may be a vaccum leak?
Is it possible it is a clogged fuel filter or something directly related to fuel supply?
A possible problem with the fuel pump relay thingy? (I think it is the relay located in front of the klima relay on the 190E).

Which is the best place for me to start? Is there any other areas I should look into?