Yesterday I changed wires and coils...last night i started noticing a stumble at Idle (and only at idle).. engine appeared to miss randomly and slightly but no pattern...also, cluster lights were flickering.....

Pulled the codes,,,all came back fine except for code 9 on pin 8 HFM .....something about high voltage?

What should I look for?

Since last week, I have changed wires, 2 out of three coils, voltage regulator, and OVP......I had the battery and alternator tested today at autozone..everything seemed fine........I don't want to go back and replace everything with the old parts unless i have to.....

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1993 300E, 2.8 M104 .....