A rich or lean condition code is a catch all code. That means it could be many things or just one.

First having a weak ignition system can cause misfires. Bingo rich and then lean.
You say you have a slight miss.... How long since you cleaned the terminals of the distributor? Change wires or plugs? What brands are both?

.6 volt sounds normal for the sensor but you should see it varying up and down a few tenths all the time. If not, it may have become LAZY on responses.
If you have miss fires it might just be smutted up!

The missing speed signal could be from a bad connection terminal on the back of the speedometer.

The ECU gets it from there or the circuit there. The ECU uses that signal in the program to do various things emission wise. If the car has an EGR it will know if the car is idling or going down a grade with the throttle closed.
If you have a delayed responding EGR (leaky) that might cause a slight miss. Back to the catch all code! Usually if its bad enough it will trip its own code and light by itself.

Having the light on is saying it has an emission problem but you have to go down a chain list of combustion order to scratch off one by one. Firing of the plugs being first!


Past that,it might fix itself by burning cleaner!

Good luck and ask questions because we have all had that dreaded CEL !
I got a car for a nice price because of the valve on the fender, that hooks to the EGR, failed to turn it on! They got tired of throwing money, through an independent shop, at the CEL !

Phil