1988 190E, that has been pretty much off the road for 4 years while I have worked on and off on it.

So here is the symptom:
starts instantly, idles OK. Off idle throttle response not as strong as it used to be. Looses power when the throttle is opened. When the economy gauge drops to halfway, it bogs. Will not rev past 4000.

New plugs, wires, cap, rotor, fuel filter, air filter.
Ran the fuel pressure test with the proper gauge, 5.5 Bar system pressure. 4.9 bar lower section pressure.

Thought it might be a clogged tail pipe, I opened up the exhaust and made it into a clean through pipe, and left the rear section disconnected after the resonator.

I disconnected the O2 sensor (I am replacing it tomorrow) but thought that is an interesting test, it would be all mechanical rather than listening to the sensor. Still ran the same.

Tomorrow I will try the LED box and duty cycle test. I am not clear on which connector to put the LED box in - this is a 1988 190E 2.3 4 cylinder, automatic. Is the plug on the passenger side by the battery or on the driver side mid fender?

Is it meaningful to look at the duty cycle when I don't have the O2 sensor connected? Or am I better off installing it and hoping for a shot at a good setting?

I am thinking about clogged fuel injectors. I once made a pressure test rig using the air compressor, for a 1978 280SE, I could try to recreate that. If it is a clog I am looking for, and not dribbles and leaks, would it be valid to pull one injector at a time, reconnect to its fuel line, disconnect the spark plugs, and crank the engine to see what the spray pattern looks like?

Or same setup, but start the engine on three cylinders to get a more realistic test than a cranking test?

A lot of wit's end here, I have to get this thing finished and this poor running is the only thing keeping it off the road.

All ideas welcome!

David