Question about 1990 Chevrolet C1500
High CO and HC at idle means in most cases that the catalytic converter is worn out, also very contaminated engine oil can cause this as well as factor's like the engine running cold due to a faulty thermostat, so replace the thermostat, change the oil if needed and replace the cat converter and it will most likely pass, my experience? 35 years as a Class A smog inspection and repair technician at a GM dealer.
Posted on Jul 21, 2010
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Posted on Jan 02, 2017
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