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Unread 10-25-2005, 01:55 PM   #1
blueliftedjeep
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Bad IAC motor??

What would be a good indication that you have a bad IAC motor? what type of symtoms would i experience? i have had a few idle issues as of late. My rpm's like to hang around 1500 inbetween shifts or when i put the jeep in neutral to coast to a stop. as my speed is reduced and i am coming near to a full stop, the rpms will dip down to around where they should be. I replaced the TPS sensor, but that was not the problem. could this be a bad IAC? or will a bad IAC cause different problems?

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Unread 10-25-2005, 02:31 PM   #2
biohazardbill
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Symptoms would include an irratic idle... somtimes high.... sometimes low... sometimes just right. This is an indication that the plunger on the iac is sticking. Try pulling it out and cleaning it up... see if that helps. Alot of times it is just gunk that has built up on the plunger causing it to stick.
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Unread 10-25-2005, 02:39 PM   #3
blueliftedjeep
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I thought that it may be the plunger as well, but i already pulled the IAC off and sprayed everything down with some carb cleaner..
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Unread 10-25-2005, 02:42 PM   #4
blueliftedjeep
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I do notice though that when the idle is sitting at around 1500 rpm, if i flick the idle up with my foot to around 2000, it will usually settle down to the proper idle
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Unread 10-25-2005, 02:45 PM   #5
biohazardbill
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Did you also clean inside the housing where it sits?
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Unread 10-25-2005, 02:48 PM   #6
kowalsy
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I did. that little black plunger was as good as new looking. Just pushing on it with my finger though, i noticed that it doesn't take much for it to get off track. Meaning that if you push against it on the side, it sometimes will not fall back into place. Now i'm sure these are characteristics off all the plungers and not just mine. Just something i noticed.
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Unread 10-25-2005, 08:25 PM   #7
Mr. Notorious
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When my IAC was acting up, it just wouldn't run if I didn't have my foot off the gas. It would just stall out at a stoplight ir whenever I took my foot off the gas. I'll tell ya, that was tricky trying to brake to a red-light. Too many pedal's, not enough feet! I was able to clean it up and it hasn't acted up since then.

When my o2 was out the way out, it would idle eratically. I would just try un-plugging the o2 sensor and see if anything changes. Have you checked your codes?
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Unread 10-25-2005, 08:49 PM   #8
biohazardbill
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With a bad o2 it will run good cold... but like crap when it warms up.
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Unread 10-26-2005, 06:18 PM   #9
JPH
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Just an idea, is your throttle cable sticking?
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Unread 10-27-2005, 08:24 AM   #10
blueliftedjeep
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I kind of already thought about the throttle cable sticking. So i looked at the throttle body with everything off it, and it appears to come to a shut when you go from full throttle to no throttle.. I also think that the way the rpm's like to hang at 1500 and then slowly creap down is too consistant for the throttle cable to be sticking.
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Unread 10-27-2005, 09:56 PM   #11
RustyJP
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the easy test is to take a voltmeter and stick the negative pole into terminal A and then stick the positive into the b terminal. With the ignition on and the throttle closed, you should have a reading of 0 to 0.5 volts. When you open the throttle, the voltage should jump to around 2.0 volts. Check this and see what you get. If you are over 2.0 volts and the throttle is closed, then the motor is bad. If you are 0 volts with the throttle open then you have an open circuit in the harness and you need to find it!

Hope this helps.
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Unread 11-23-2011, 06:51 PM   #12
grivera
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Thread revival!! Iac testing ?

Quote:
Originally Posted by RustyJP View Post
the easy test is to take a voltmeter and stick the negative pole into terminal A and then stick the positive into the b terminal. With the ignition on and the throttle closed, you should have a reading of 0 to 0.5 volts. When you open the throttle, the voltage should jump to around 2.0 volts. Check this and see what you get. If you are over 2.0 volts and the throttle is closed, then the motor is bad. If you are 0 volts with the throttle open then you have an open circuit in the harness and you need to find it!

Hope this helps.
Does one need to disconnect the IAC harness to perform the above test? If so, how would it produce volts measurable by the meter? If one doesn't connect the harness, how are the terminals?
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Unread 11-24-2011, 03:52 AM   #13
jsawduste
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Quote:
Originally Posted by RustyJP View Post
the easy test is to take a voltmeter and stick the negative pole into terminal A and then stick the positive into the b terminal. With the ignition on and the throttle closed, you should have a reading of 0 to 0.5 volts. When you open the throttle, the voltage should jump to around 2.0 volts. Check this and see what you get. If you are over 2.0 volts and the throttle is closed, then the motor is bad. If you are 0 volts with the throttle open then you have an open circuit in the harness and you need to find it!

Hope this helps.
Quote:
Originally Posted by grivera View Post
Does one need to disconnect the IAC harness to perform the above test? If so, how would it produce volts measurable by the meter? If one doesn't connect the harness, how are the terminals?
The IAC harness needs to be connected. You are testing through the IAC and checking the actuator motor itself.

Another trick is to slide a business card over the ports in the TB. By opening and closing the ports you can control the air allowed to pass through the TB at idle. Just like the IAC plunger does.

One word of caution. Don`t play with the IAC plunger. I know you want to but don`t. It is "meshed" with the motor and trying to see if it is OK often ends up destroying it.

Factory OEM sensors are by far the best. A few more bucks sometimes but well worth the money.
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Unread 11-24-2011, 07:56 AM   #14
grivera
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Quote:
Originally Posted by jsawduste View Post
.



The IAC harness needs to be connected. You are testing through the IAC and checking the actuator motor itself.

Another trick is to slide a business card over the ports in the TB. By opening and
How do you make contact with the correct terminals if the harness is plugged in?
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Unread 11-24-2011, 08:02 AM   #15
oldtime_ironman
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Quote:
Originally Posted by grivera View Post
How do you make contact with the correct terminals if the harness is plugged in?
It's called "back-probe". Basically you try and stick the end of the meter probe into the backside of the connector, right where the wire is also going in. Sometimes the probe is too fat - so you can stick a sewing pin in there instead, and hook the meter up to the pins.
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