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Discussion Starter · #1 · (Edited)
05 Cobalt 4dr/auto 2.2L 220k.

Yes i know its high mileage but i got it for 400 bucks to be a work beater and its not in bad shape,

Anyways, the issue im having is a cold missfire. Once the engine gets up around 160-170* it begins running fine. It starts fine, no excessive cranking and idles smooth, and wont miss if i ease into the pedal (usually), but if its in gear moving or if i stab it in park it sounds like a machine gun.

Ive gotten multiple codes but cleared them and the only one that came back was "knock sensor low input" and a code for the fan circuit. I believe the numerous codes were from my someone doing the "unplug stuff till it runs normally" diagnostic method.

I found the blue wire on the knock sensor broke so i fixed that, now i get no codes.

I changed the plugs to no avail. It runs great once it gets warmed up. The old plugs didnt show anything alarming and look normal.

I plan on doing a compression test but it doesnt smoke and runs great otherwise.

Im not really a chevy guy and most my EFI experence is pre 97 EEC IV ford truck stuff...so im a bit lost here.

Ive read the coilpacks and ignition module are common on these to go, but ive always known this stuff to fail when warm, not cold. Ive cleaned the G101 Ground (under the coolant bottle) but the one on strut tower looks fine.

I did get a O2 sensor heater code for the downstream O2, but i havent seen it since i fixed the ground, but when i watch the live data on my scanner it doesnt do much, seems to just sit around .1 volt....is this normal? Ive never dealt with downstream O2's, the upstream one jumps all over the place.

Any input would be greatly apperciated.
 
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