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Passed Emissions at high Idle, Failed at Idle

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88 Jeep Comanche 4.0L


Exactly what the title says; i changed fuel pump/rail/regulator/injectors/ spark plugs and fixed all vac leaks so she purrs like a kitten to PASS inspection. I failed at idle, passed at high idle.


Idle numbers Reading Standard Result- Fail :grrrr:

HC ppm 227 220

CO% 5.07 1.20


High Idle numbers Reading Standard Result- Pass comanche.gif

HC ppm 24 220

CO% .20 1.20


Any ideas on the dramatic differences? Turn the idle up? replace the cat? Replace 02 sensor?

Thanks in advance

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sorry about your commie state codes! 02 is my vote... i believe in replacing them in three year or 60,000 miles intervenes like Bosch says ..... and yes another is how is your thermostat doing ?? if its stuck open cooling too much you will go rich too and talk of temps engine coolant temp sensor maybe going bad too ...grab a VOM and start testing some...

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I need to do a coolant flush anyway so ill grab a thermostat and do that at the same time; ill grab an o2 sensor later this weekend when i have the money. Ive never changed it in the 6yrs ive owned it. (in the meantime ill work on the loosening the other one and getting it out). On second thought; i may be replacing the trac-bar with this weeks money since i finally aligned it right(last week) and now i have death wobble on occasion. I have until 3-11-11 to fix the emmisions but it sucks cause i just had the exhaust re-welded with a new muffler put on. Its goin to suck if i have to do a new cat, if i do I'm gonna run a stack through the bed this time. Then probably have them fail me for that. In the great communist state of New Jersey; who cares if my numbers are high at idle, i don't want to be idling; i want to be driving. comanche.gif

Thanks for the help and Ill keep you posted :)

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