Hello-

I've had a misfire problem at idle for a while with my '96 I4. I've tested sensors and injectors with a multimeter. Replaced the coolant temp for fun. Done the routine stuff (plugs, wires, coil, oil change, coolant flush...). Still get P0304 and a flashing CEL mostly when the car is sitting in park or neutral and sometimes at a stop light. I just checked the transmission range switch (auto trans) and it seemed to be OK.

I put the multimeter on the battery and with the car running but everything off I get voltage that jumps between 13.30 and around 14.01. The jumps are all over the place though. One second it's over 14.0 then it'll dip to 13.8 and maybe stay around there or go lower then jump higher. All the while the CEL is flashing. Is this normal?

As soon as I switch on the AC fan the voltages seem to smooth out and stay around 13.75 to 13.8. The CEL stops. My datalogger shows timing advance jumping anywhere between 0 and 12 degrees when misfiring but it stays around 5-10 with the AC fan.

Could I be looking at a bad ECU or altanator? Or should I forget about the voltage and start looking a maybe a bad headgasket or something else in cylinder 4? I also added a homemade grounding kit hoping it would help but it didn't.

Thanks for any help.