1986 Honda Civic High Idle HC

IRISHMUSTANG

MEMBER
7 POSTS

I have a 1986 Honda Civic DX 4WD manual trans with a carburated 1500cc engine. It has 156,000 miles. The first smog test it failed HC at idle with 179 (120 is max allowed). It passed at 2500 rpm. So I changed the plugs, cap, rotor, air filter and the breather filter. I also pulled the egr valve cleaned off the carbon and vacuum tested it. It holds a vacuum. I checked and corrected the idle speed and timing. I took it in for a retest and the HC are down to 139 at idle, thus it still failed. After telling the tech the work I did he suggested a new catalytic converter. Is this my best bet, or should I try a new O2 sensor first?

Mar 19, 2007 at 6:50 PM

BRUCE HUNT

✓Experienced Mechanic
3,754 POSTS

I would opt for the O2 first and then see how that comes out. Less money, however, they usually work fine or fail. Whereas, the convertor can be slowly plugging and losing efficiency. Your call & $. You seem to actually have things well in hand. Good job.

Mar 20, 2007 at 2:37 AM

Suggested Repair

Try a new oxygen sensor before replacing the catalytic converter. An O2 sensor is less expensive and typically works or fails outright, while a converter can gradually lose efficiency.

Conversation Summary

A 1986 Honda Civic with a carbureted 1.5L engine failed a California smog test for high HC at idle, then improved but still failed after plugs, cap, rotor, filters, EGR cleaning, and idle and timing checks. It passed at 2500 rpm. The test tech suggested a catalytic converter, while the expert recommended trying an oxygen sensor first because it costs less.

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1986 Honda Civic High Idle HC

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