Failed smog; very high HC @ idle, other levels pass. All pass at 2500rpm

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11-16-2019, 02:18 PM

#16

wpatters1229

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Model: Cherokee

Quote:

Originally Posted by lawsoncl

Don't use the screw to monkey with the idle. The IAC controls the airflow to control the idle. By mucking with the screw to bump up the idle you're effectively creating a vacuum leak. On the restest, make sure the car is good and warm for the test. Sometimes you sit and the engine and cat aren't fully up to temp when they do the idle test.

Well, I did you are right...it took a while but it did adjust back to what sounds like normal speed. What if it goes back to fully closed? Will it adjust to run the right speed and eliminate any chance of a vacuum leak?
Not sure how to adjust back to normal? Is there a factory gap in the butterfly that you have to obtain or is it all controlled by the IAC?

Thanks

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11-16-2019, 02:24 PM

#17

97grand4.0

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Year: 1997

Model: Grand Cherokee (ZJ)

Engine: 4.0, new lifters valve job with new springs and exhaust valves, preload set with shims

Apparently you did not see my post #7. With no scan tool, you are basically blind trying to solve this kind of a problem. You should have a scan tool for an OBDII vehicle any way. Go get one. They are cheap enough and you can get one with graphing on Ebay for about $30.

The IAC will control the idle to a set speed until you go out of that range with the idle stop screw, at which point it is no longer able to.

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11-16-2019, 04:07 PM

#18

lawsoncl

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Year: 1989

Model: Comanche (MJ)

Engine: 4.0

Quote:

Originally Posted by wpatters1229

The IAC allow air to bypass the butterfly valve. If it's idling okay, and you didn't adjust it too much you're probably fine to leave it that way. Here's Cruisers info on setting the idle stop on a Renix. I think the HO engine has the same 0.003" gap setting. http://cruiser54.com/?p=94

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11-16-2019, 05:51 PM

#19

wpatters1229

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Model: Cherokee

Quote:

Originally Posted by lawsoncl

I read that and understand except he mentions you need to Read just your Throttle Position Sensor. Did not know there was any adjustment on that on the jeep 4.0 engine.

Thanks

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11-16-2019, 05:54 PM

#20

wpatters1229

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Model: Cherokee

Quote:

Originally Posted by 97grand4.0

Of course what any tech would need to answer your question would be to look at your scan tool data.
What are your short and long term fuel trims?

This is a 1993 and to my knowledge, there is no place for a scan tool. To see the error codes you have to do the turning the key 5 times etc.. This car has no error codes.

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11-16-2019, 09:25 PM

#21

lawsoncl

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Year: 1989

Model: Comanche (MJ)

Engine: 4.0

Quote:

Originally Posted by wpatters1229

I read that and understand except he mentions you need to Read just your Throttle Position Sensor. Did not know there was any adjustment on that on the jeep 4.0 engine.

Thanks

The older remix tps had slotted holes and could be rotated to adjust it.

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