3100 engine problem

[Azrael]

The lean condition sounds like a symptom of the misfire. The O2 sensor will read the unburned oxygen of the misfiring cylinder and show a lean condition. The PCM will then try to compensate by enrichening the fuel/air mixture which would cause the poor economy. Did the misfiring code point at a specific cylinder(s)? If so, try moving the coil packs around and see if the misfire moves to another cylinder. That will tell you if a coil is dead. If it doesn't you'll need to do a compression test. If compression looks good then I'd suspect the ignition control module is bad.

When you changed out the E3 plugs, did any look different from the others? Black/wet ones usually point to a misfiring cylinder.

Ruling out a clogged exhaust is easy. Pull the O2 sensor out and run the engine for a few seconds. Just long enough to see if there's a change in idle quality.

[gmmalibu]

when i had the codes checked it showed a po305 and a po420 which was a cylinder 5 misfire and a malfuctioning cat-converter, i replaced the plugs n wires back to ac delco but all the e3 plugs i pulled out look ok a bit yellowish brown,how ever there were two plugs which had the tip smaller than all the other ones, but now the car has a new issue it dies and shuts off everytime i turn, i have to drive with my foot on the brake and gas at the same time to avoid the car stalling and turning off when i turn in any direction.

how do you check ignition coils?