Are you sure that you have a running RICH code ? You may need to look into your O2 sensors…some vehicles cannot even run when the Pre Cat o2 dies…it no longer knows how to fuel itself. The o2 sensors help the engine run as lean as possible without damage to the engine…when they fail…in some cars the computer defaults to run as rich as possible because this is the safer of those two evils of Rich and Lean… You can almost always run rich…but not so Lean. But this is not so common… I would be looking at the engine timing.
In my experience whenever I have multiple misfires…it is either a vacuum leak (lean)…OR it is due to T-Belt Stretch…and thus…the mechanical timing of the engine. When a t belt stretches or jumps a tooth the timing of the ignition as well as the fuel injection are off…and they usually head in the Retard direction meaning late. When this occurs…the plugs do not fire at the right times (late)…and the fuel injection sprays later than wanted as well. This results in multiple misfires as well as a Rich condition due to not enough time to burn the fuel charge
The FIRST thing I would be checking are my timing marks…Line up the crank to TDC and notice where the Cam is timed…If you see a discrepancy…you found the problem. DO THIS FIRST…then move on…I doubt you will move beyond this however
One tooth off or stretch of the T-Belt can and will cause everything you are seeing