I am new to this forum and need help troubleshooting to get my 1990 LX with 160K miles to pass TX state emissions test. Test numbers are as follows:

High Speed (1904 RPM)

Reading
HC (ppm) 52 PASS
CO (%) 1.01 PASS
CO2 (%) 13.9
O2 (%) 0.1
NOx (ppm) 507 PASS
DILUTION (%) 14.9

Low Speed (1810 RPM)

Reading
HC (ppm) 56 PASS
CO (%) 1.24 FAIL (allowable 0.98)
CO2 (%) 13.8
O2 (%) 0.1
NOx (ppm) 585 PASS
DILUTION (%) 15.0

Engine runs great - with no apparent issues. Has clean air filter, fresh engine oil and filter, new plugs, timing is on spec., spark plug wires test OK. No check engine light. I have recently run fuel system cleaner (techron) and have cleaned out the throttle body and intake. Car has been sitting and not driven much.

Does anyone have a list of potential things to check to lower the CO?

Thanks!

 

Recommend you inspect and clean the PCV or replace if necessary.

Inspect carefully for intake leaks in vacuum lines, intake manifold, PCV, etc.

If O2 sensor is old or never been replaced, replace it. A slow O2 sensor could cause rich condition at idle that might disappear at higher speeds.

good luck