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Consider that you could have a significant vacuum leak. The FI system may adapt to it when warmed up*, but the sudden acceleration shoots in slug of extra air (which is all the "gas pedal" provides) makes the already lean mixture too lean to run smoothly.
*When cold, the extra fuel provided by the ECU for cold running could be "masking" the false air sneaking in unreported by the AMM.
I use Propane to test for vacuum leaks. It's less messy—and no more volatile— than carb cleaner or other sprays. Take the nozzle tip off a propane torch and replace it with some snug fitting rubber hose about 2 feet long. Practice with the valve to get a moderate gas flow (not a roaring blast).
With the engine at a warm idle, open the gas valve and poke the end of the hose around each injector for a couple of seconds. If the seals leak, you should hear an RPM change when the propane gets sucked in and burned**.
Do the same around any other suspected areas, like hidden vacuum hose ends — and don't forget the intake manifold gasket itself.
To block the breeze from the (240) fan, lay a piece of cardboard from the fan shroud to the engine
**If you use a Digital Volt Meter to "read" the O2 sensor output voltage (O2 signal wire disconnected from ECU), you'll see the signal voltage rise instantly if any propane gets drawn in.
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Bruce Young
'93 940-NA (current), 240s (one V8), 140s, 122s, since '63.
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