Engine Performance problem
1994 Ford Ranger 4 cyl Two Wheel Drive Manual 171000 miles
2.3L dual coil non-distributor EEC IV set-up.
Tach acting erratic, idle rough only at op temp and finally threw a check engine light with code 222 and 224. Sometimes tach shows no rpm at all while idling.
Have replaced plugs (gapped at 0.43), plug wires, coolant temp sensor, coil packs and all wire connections/connectors visually seem in very good shape and condition. Now only code 222 shows. KOEO passes with a 111 now, but KOER shows a 998 fault and then 222. Tach still erratic and idle no better than before. Runs smooth above idle, starts fine with engine hot or cold.
What's left in my thoughts as the cause:
22k ohm wire bad, if equipped. Condenser/capacitor on one of coil pack mount bolts bad. ICM, PCM or CKP (those three each are expensive to replace as a guess). How can I narrow what's wrong to the actual failed component without replacing all what I believe left to try?
Any other thoughts, diagnosis and self-tests with procedures will be greatly appreciated.