After shutting off the key the shut off lever will not reset to where i can restart the vehicle until I completely cycle the key from off to start 3 times. Is this due to a week spring somewhere? Or would it be somehow holding vacuum?

Thanks for any advice.

The lever should stay down indefinitely until you turn the key to the run/glow position. As a quick test, after shutting off the engine, disconnect the vacuum line at the shutoff actuator. If the lever springs up, the problem is upstream, likely the vacuum valve at the key switch. I doubt the lever will stay down because cycling the key won't release sticking inside the IP.

Sixto
87 300D

has any vacuum lines been disturbed recently? you may have put the brown hoses back in the wrong position...

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1987 300TD
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The key switch valve has 2 ports you can see but really there are 3. The third vents to atmosphere behind the dash.

It is a 3-way valve not a simple pass/block valve. I will try to stay away from electrical terms because open and closed mean different things to pneumatics than electrical.

The valve has a common port (that goes to the actuator) and two switched ports. There is a path between the common and the supply port (that goes to your vacuum pump) when the key is off.
There is a path between the atmosphere port (no hose nipple, it's just a hole in the valve) and the common when the key is on.

The actuator is arranged such that atmosphere = run and vacuum = stop.

When the engine is supposed to run, the shutoff actuator is connected to atmosphere and the supply line is blocked.

When the engine is supposed to stop, the shutoff actuator is connected to the supply line and the atmosphere port is blocked.

If you were to get those brown two lines swapped at the key then the problem you describe would occur.

In this case the supply goes to atmosphere when the key is on (creating a vacuum leak) and the actuator line gets dead ended.

When the key is off, the actuator is connected to the supply so it still shuts down properly.

If your vacuum system is tight, the vacuum won't bleed down until the next time you start the car. Then when you turn the key on, the actuator gets dead ended, instead of being connected to the atmosphere port, so it cannot bleed down. This prevents the actuator from releasing the rack until you cycle the key enough times to bleed off all the residual vacuum. Then the actuator is released and you get fuel, which allows the engine to finally start.

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2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Thanks everybody for all the excellent info! I did change the ignition switch a while back so the swapped lines is my most likely problem. I really appreciate the detailed information on this system. Really helps me to understand in my head what is happening.