1990 300SEL Cold Start Problems

[Qrash]

Cold Start Problems 1990 300SEL:

My search attempts did not reveal anything quite like the symptoms I am experiencing. The vehicle has 175,000 miles, just passed PA state emissions with no problem, consumes about a quart of oil per thousand miles (for the last 100,000 miles) and I have recently run several treatments of Techron. I replaced a leaking EHA valve at about 145,000 miles plus new ignition wires, rotor and cap at 160,000. Standard copper-tip spark plugs new.

When the vehicle has sat unused (and cooled) for four or more hours, it takes several attempts to start the vehicle. The problem has worsened over the past month and is exacerbated somewhat on cold mornings (now about 45 deg F). Two or three times in this last month, it has started, idled and run fine while cold, but the intermittent good starts have "gone away." I have tried one of the recommendations (turn ignition on for about five seconds before starting). No change.

Symptoms:
1. First start attempt ... motor kicks over, runs about two seconds and dies.
2. Second start attempt ... same.
3. Third start attempt ... same. For the first three attempts, if I attempt to apply throttle it also dies.
4. Fourth (or sometimes fifth) start attempt ... engine starts and runs as long as sufficient throttle applied and let it warm while holding at about 2000 rpm.
5. If I let the engine warm at 2000 rpm for about 3 - 4 minutes, everything is fine and the car runs and idles perfectly thereafter.
6. If I do not let the engine warm for 3 - 4 minutes and release the throttle, it will buck at about 500rpm ... sometimes dies and sometimes will warm and smooth out to regular idle at 700-800 rpm.

I have located but have not otherwise inspected or tested the cold start valve. Could this be the sole culprit and, if affirmative, is there a way to positively diagnose prior to replacement?

Other considerations / tests / diagnosis? ... Thanks much, Qrash

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