Cold Start Valve 190E 2.6L 1989

Car won't start without pumping gas pedal, so was advised to replace cold start valve. (Car seems to run well once started, and idles down to normal within a few seconds of starting; only other thing I see is
sometimes sluggish accelerating away from a stop until the revs get to 1500 to 2000 range, then acceleration is very solid and quick.) Web sites selling parts show 2 different O-rings that should be used with replacement of cold start valve. Is this something I can do in my driveway? That is, given the existence of the O-rings, when I loosen the 12mm fitting on the top of the valve, is the fuel in the line under pressure? I had some difficulty busting loose the two 5mm hex head bolts that anchor the valve to the block, but that is out of the way. Anything I should be aware of before continuing? Do I need to prime the line in any way when reassembling? If I replace the valve and it still won't start without pumping the pedal, what should I look at next? Thank you for your time and input.
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There's the electric valve and then there are the components that switch the power TO the valve. Have you checked if power is at the valve when cold starting - about 11 v.)?
The fact that the engine starts and then idles down within a few seconds suggests that the cold start system is working.
Sluggish acceleration is completely separate from the cold start system.
Fuel IS under about 45 psi pressure.
IMHO, the question ought to be: Why is pumping the accelerator (of this fuel injected engine) necessary for it to start when cold? (There's no choke to close or accelerator pump to squirt extra fuel into the engine - so why does pumping work?)
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Good information for pursuit and I agree, it is curious pump of the pedal is necessary (should have mentioned that with the engine fully hot, if it is turned off for more then several minutes, have to press pedal again). I'll see what I can find on the electrical end. Thank you for your time.
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Unless that valve is leaking into the engine, I doubt it is the problem.
More than likely, the fuel pump relay is bad or the thermotime switch is bad. Both control power to the cold start valve.

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Good insights I had not considered; will see what I can find. Thank you for your time.
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