Fuel Pressurization Puzzle

[EricSilver]

Car: 1989 260E
187,000+ miles

Scenario 1: First Cold Start of the day, or Cold Start After Sitting all Day

Turn key, engine fires up immediately and idles smoothly.
If I immediately begin driving, depressing the accelerator does not produce instantaneous acceleration. It feels as if fuel is only trickling in.

-- HOWEVER --

If I warm up the car for about two minutes, maintaining about 1500-2000 rpm, that fuel starvation feeling does not occur and the car behaves normally.

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Scenario 2: Hot Start After sitting for about 30 minutes
Turn key, engine cranks for about 3 to 5 seconds before firing normally. Idle tends to be lumpy. Higher revs are smooth, but acceleration seems a bit sluggish – again, as if fuel injection is not at peak.

I get the impression that one cylinder is misfiring because the feel and behavior has been so consistent. I know that the fuel/air mixture is a contributing factor but not the whole of the problem. The other potential culprits are:

* Dirty Fuel Injector
* Dirty Fuel Filter
* Faulty O2 Sensor
* Faulty Fuel Accumulator
* Faulty Fuel Pump(s)
* Vacuum leak (I have been experiencing hard shifting lately)
* Faulty Fuel Pump Relay
* Over voltage Relay (It is actually fairly new but since the OVP is
blamed for practically everything else, why not include it here.)

I welcome your good comments.