I am experiencing an idle issue with my 2003 Chevy Cavalier 2.2l EcoTec. Vehicle has 219,000 miles on it and has ran great up until about a month ago when I started to get a rough idle when I would cold start the car. The best way to describe the issue is that the rmp needle would drop a few hundred rpm for a very brief moment before returning to normal. This will happen several times before completely subsiding at operating temp. I can repeat the issue while idling at operating temp when I engage the a/c compressor. The car almost stalls at times and the lights dim slightly when this occurs. One CEL code "P0420". No loss of power although car seems to shudder forward sometimes when pressing on the gas after idling.
I didn't find the right solution from the Internet.
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