Starting problem
 

This is related, perhaps, to the New Guy problem. I park my 1984 380 SE in my sloped driveway, and when I go out to start it in the morning, it turns over immediately but stumbles when the accelerator pedal is depressed. I pump it a few times, then it is OK, and I can drive off just fine. This happens only after the car has sat for a long time, like over night. It starts and runs fine, like a champ, in fact, the rest of the day. Car has a relatively new fuel pump and filter; plugs are fine; plug wires are relatively new. Also had new idle control switch installed about six months ago. Any ideas, folks? Thanks.