Engine runs rough and stutters when gas is applied, runs normal when idling. Problem shows up only when car was not used for more than 12 hours and is worse the longer it was not used. ''Check engine light'' was on one time with failure code for ''catalytic converter defective (possibly caused by engine misfire or vacuum leak or engine oil leak into exhaust valve)''. Cat converter was exchanged and failure code disappeared but engine runs still rough and stutters - so cat converter might break again soon. What is the reason?
Start by replacing the plugs and plug wires, this is esp true if car has over 100,000 miles on it. damp air can make the problem worse.
Testimonial: "helpful"
Your cat should last quite a while now it is replaced. I recommend testing coil packs and module. Change plugs and wires and double check your vacuum hoses.
Testimonial: "Helpful hint"
You might even try changing the fuel filter...when you let it idle it is getting enough gas to run and when you give it gas you might not be getting enough fuel through the filter to keep it running...
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I forgot to mention, engine computer was changed, too - problem is still there.
Is it possible that spark plugs and wires can cause problems only when engine was not running for some/longer time ... maybe because of humidity crawling somewhere?
I would replace the spark pugs and wires for a start.
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