Vintage Cars: 1978 450slc, throttle position sensor, fuel pump relay

Question
My 450 has 122000 original miles, the car sat for approimately
7 months without being started or driven it ran fine before
that. I was unable to get the car started so I emptied out the
old gas in the tank, replaced the fuel pump and fuel filter,
and cleaned the injectors.  The engine will idle but dies when
you try accelerate.  Any suggestions?

Answer
could be several reasons.
Your fuel regulator could be gummed up or not functioning
A vacuum leak ( these are vacuum driven systems ANY leak can wreck havoc)
Is the idle even? does it die when you hit the gas? or after it revs a second or two.
Are you sure the air intake( throttle plate) is moving?
Throttle position sensor is another possibility.
with key on ( car not started)  move throttle plate open , you should here distinct clicks
Have you pulled a plug, are they gas fouled? ( wet)  Can you smell gas?
Can you hear the fuel pump pressurize system?
Last thought - fuel pump relay going bad?

With some  answers to these questions I may be able to help more
Good Luck
Ron