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I have a 98 sunfire with a 2.2 auto with air. It runs OK, but then every now and then it just stalls. A mechanic told me it might be a MAP sensor. I hooked up an actron scanner and the car has no codes. If a MAP sensor was causing the car to stall would the check engine light not turn on and would it not set a code? I'm leaning towards a good tune up and a new cat. convertor. The car has 140,000 miles on it. I think the convertor is original. Would a plugged convertor set a code too or not?

Thanks Marc