I can't emphasize enough the value in making the simple, non-intrusive test I mentioned above. Not only does it give the first step in a real diagnostic test, but it also gives a feel for what is happening in the system.
Don't be afraid of it, go try it. Press slightly, more slightly, heavily, more heavily. It will kill the motor. Obviously at a point between slightly and more slightly you overcome the feedback electrical control and as you go heavy you flood the motor. You won't hurt anything doing this at idle a number of times. You can overheat the catalyst by continuously overwhelming the feedback control, though.
There is a sensitivity to be learned here and if your feedback system is already overwhelmed you won't see the compensation. If single cylinder mixture defficientcies are responsible for your rough running (and this is VERY common)you will see a smoothening instantly, when pressed, which goes away if the plate position is held ridgidly (as the system corrects your movement). My first step in diagnosing a K-jet car is to do this process. I WANT to see if basic mixture either richer or leaner affects the problem. The answer is just a start, but, this feel needs to be felt by anyone who wishes to understand these systems with test equiptment.
Bosch Master, ASE Master, L1
33 years MB technician