It sounds unlikely that it's ignition (points, cap, plug wires) related, or it probably wouldn't smooth out when warm. Slight chance it's got the wrong heat range of plugs. Are they the right ones? I don't know that the platinum or wierd electrode type ones really work very good in those engines. They never did in my B20 (4 cyl.).

Here's a few other ideas:

Pull plug wires and reconnect them one at a time while running cold to see if you can find a cylinder or two that are sick (or somewhat uneffected by the plug wire removed).

If you find a weak cylinder, try swapping plug wires, plugs, injectors with other cylinders to see if the problem follows a certain component.

When you had the injectors "serviced" did that include new seals? I've never done it myself, but I understand there are a couple different seals on them...something about a seal between the base and the head being a bigger problem than the one on the injector itself. A leak here could close-up as the engine warms. Someone on the board said they sprayed soapy water around the base of the injectors to detect leaks.

A leaky intake manifold gasket can also be worse when cold than hot. You can squirt some sort of oily stuff like WD-40 or maybe a little thicker lubricant around the manifold-to-head mating point and see if that temporarily smooths it out. It may be hard to hit the bottom side of all the tunnels though. You might make sure the nuts are all snug, but be careful...the studs are probably rusty and brittle.

A bad throttle position switch will hamper acceleration, particularly with a cold engine. Snap open the switch and clean the contacts with some alcohol and a pencil eraser. If the contacts look well-worn, you can carefully tweak them to track down a fresh "path". If it looks like the printed board areas are worn clear through, you might have to replace the $witch. Haynes manuals spell out the testing and adjustment of these switches pretty good.

That's enough for now..let us know how it goes.