Stan,

I'm don't know what you've done so far in diagnosing your problem so some thoughts and ideas ....

D-jet CPU's don't fail. Well. OK, it's VERY rarely.

Yes, good idea to pull one plug wire at a time while idling to find which one(s) doesn't (don't) deteriorate the idle much.

You can pull all the plugs, reconnect them to their respective leads, ground the plugs, and crank it over to check for spark. A timing light is nice to use as it allows you to sample each individual plug wire while the engine is running - looking for the spark to "skip a beat" here and there.

Are all of the plugs looking to be burning at about the same color? Or is one of them way sootier or way lighter in color?

You could have a leaking intake manifold gasket or leaking injector seals. You can read up about testing those areas with a unlit propane torch.

If you find three cylinders running well and three sickly, then must likely one of the trigger contacts isn't opening.

As you suspected, a clogged injector is possible. I rigged some clear plastic tubes that fit tightly on the injector tips, were plugged on the opposite ends and had little screws that act as drains.





Once the injector rail was all connected back up to the car, I pulled the distributor out of the engine and removed the cap (left the rotor in place). The trigger contact wiring was still connected to the distributor. I turned the ignition on (the fuel pump will run) and spun the distributor rotor as fast as I could with one finger. The injectors will squirt-squirt-squirt. Since there is no vacuum acting upon the manifold pressure sensor (MPS), you will be simulating a command for a highly rich condition. So the tubes should start filling with fuel, and hopefully at an equal rate. If you connect a long vacuum hose to the MPS and you suck the sensor diaphragm down while spinning the rotor, you "may" be able to detect a reduction in injector flow, but don't worry if you can't - this is a rather crude test. Also, by sucking on the MPS port, you can detect if the diaphragm is shot. If the MPS doesn't hold a vacuum it will cause an extremely rich running condition.