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Old 04-28-2012, 10:34 AM   #1
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Default 04 GP GTP Hard Idle

Where to begin?
I'm getting a hard idle and throwing a P0300 code. She runs normal above idle with no acceleration delays. Occasionally I'll get the cat in danger blinking engine light. At idle on the scanner, cylinder 1 misfires on every cycle at idle and 3 misfires often.
I've replaced 'some' of the usual suspects; plugs, cables, mass airflow sensor, and fuel filter with no improvement. I'm thinking maybe a vacuum leak or a clogged cat?? ...but with no acceleration delays and no rotten egg smell, I'm leaning away from the cat being bad.
Without a smoking gun, it was suggested that I continue to replace the usual suspect parts by cost until the problem goes away. So, I'm thinking O2 sensors, coils, fuel pump and cat, in that order???
I'm in Germany with no Pontiac mechanics so my technical resources are limited...
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Old 04-28-2012, 12:19 PM   #2
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P0300 is random misfire. Then with 1 and 3 showing up and you already changing plugs and wires. I would look at your coils. Make sure everything is clean under them. A vacuum leak should give you a P0171 code and make you run lean. I would still look around for one, but woudl still start with the coils.
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