Engine idle surge from 750 down to 250 then back up! - JeepForum.com
 
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post #1 of 10 Old 06-12-2013, 04:07 PM Thread Starter
brewcity1
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Location: Milwaukee
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Engine idle surge from 750 down to 250 then back up!

Hey guys...just got the 9er home, and stopped to get the mail. I noticed that when in park, the engine was surging from normal idle position of around 750 RPMs down to 250. It just keeps going up and down within that range. I then put it in Drive...and it dropped even lower, and still surged, and almost cut out.
I have a new IAC and a new TPS, as well as a new coil, cap, rotor, and wires.
I just replaced the plenum gasket over memorial day.
Any idea's what I should check? This is the 1st time this has happened. I did look for a vacuum leak, but heard and saw nothing.
Thanks for the help!


2004 Grand Cherokee Limited 4.7L
General Grabber AT2's 255/65/17
1" Addco rear sway bar
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post #2 of 10 Old 06-12-2013, 04:15 PM
Candymancan
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Its probably that IAC and or TPS you replaced.. Shut off the engine and turn it back on.. Does it go away ? If so its probly the IAC i bet.. Do you still have your old one ?

2013 6.2 V8 Camaro SS 30k
98 5.9 V8 ZJ 180k
98 4.0 I6 ZJ 240k
90 5.9 SJ Grand Wagoneer 110k
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post #3 of 10 Old 06-12-2013, 04:16 PM Thread Starter
brewcity1
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Quote:
Originally Posted by Candymancan View Post
Its probably that IAC and or TPS you replaced.. Shut off the engine and turn it back on.. Does it go away ? If so its probly the IAC i bet.. Do you still have your old one ?
Lovely...OK..I'll go out and start it up and report back. Dont have my old one
Thanks

2004 Grand Cherokee Limited 4.7L
General Grabber AT2's 255/65/17
1" Addco rear sway bar
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post #4 of 10 Old 06-12-2013, 04:19 PM
Candymancan
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My 5.9 has been doing this for awhile actually... I am just too ****in lazy to replace my IAC... I took a 220 miles the other day.. got 18.3mpg which was pretty damn impressive lol at 55-70mph.. But anyway when i got to the city and stopped i noticed my idle whirring from 200-750 up and down up and down.. So i put the Jeep in park turned it off and then back on and it idled fine.. It does this sometimes randomly not alot very little but its done it maybe 10 times in the last 3 years lol.. Sometimes it will go to like 1200 rpm and sit there.. so i shut it off and on and it works fine... I replaced my TPS with one from a JY 5.9 and it hasnt done that anymore but the surging yes.

I also read somewhere the first O2 sensor can cause this too.. I dunno how but i read that a few times actually

2013 6.2 V8 Camaro SS 30k
98 5.9 V8 ZJ 180k
98 4.0 I6 ZJ 240k
90 5.9 SJ Grand Wagoneer 110k
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post #5 of 10 Old 06-12-2013, 04:50 PM Thread Starter
brewcity1
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Quote:
Originally Posted by Candymancan View Post
I also read somewhere the first O2 sensor can cause this too.. I dunno how but i read that a few times actually
Well...I do need a new Cat and O2 sensors for sure. Cat and muffler are shot!
I started her up again...and the surge did go away. I'll let it cool...start her up again, and let her get to operating temp to see if it changes.
Thanks a lot for your info...I appreciate the help!

2004 Grand Cherokee Limited 4.7L
General Grabber AT2's 255/65/17
1" Addco rear sway bar
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post #6 of 10 Old 06-12-2013, 07:02 PM Thread Starter
brewcity1
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I actually took off the IAC, and cleaned out the throttle body where it connects...and it was really dirty...tons of carbon!
The IAC wasnt too bad at all though (and is a Mopar part). I started her up, and let her idle...so far so good. No surge.
If it starts up again...do I need an new IAC or what?

2004 Grand Cherokee Limited 4.7L
General Grabber AT2's 255/65/17
1" Addco rear sway bar
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post #7 of 10 Old 06-14-2013, 04:12 AM
Candymancan
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Im not exactly sure.. I know mine did it again yesturday except this time when i stopped and parked the Jeep the idle went to like 1300 rpm.. Shut it off and turned it back on and it was fine... Something sure is fishy.. Altho my IAC is original and so is my TPS.. I just dont have the funds to buy new ones.

2013 6.2 V8 Camaro SS 30k
98 5.9 V8 ZJ 180k
98 4.0 I6 ZJ 240k
90 5.9 SJ Grand Wagoneer 110k
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post #8 of 10 Old 06-14-2013, 08:12 AM
PolkaPower
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Just go to a JY and get some used ones fo cheap G
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post #9 of 10 Old 06-14-2013, 02:44 PM
dougmorgan99
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I have been fighting this for about 8 months now... New O2 sensors, IAC, TPS, plugs, plug wires, vacuum check and pcm connector check. Other days its fine, other days crazy idle... . So not consistant to easily troubleshoot. Next step is MAP, then PCM, etc, etc. It is fustrating.
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post #10 of 10 Old 06-17-2013, 07:23 AM Thread Starter
brewcity1
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Quote:
Originally Posted by dougmorgan99 View Post
I have been fighting this for about 8 months now... New O2 sensors, IAC, TPS, plugs, plug wires, vacuum check and pcm connector check. Other days its fine, other days crazy idle... . So not consistant to easily troubleshoot. Next step is MAP, then PCM, etc, etc. It is fustrating.
Can you keep us all updated on this please...we would really appreciate it.
Yeah...SUPER frustrating!

2004 Grand Cherokee Limited 4.7L
General Grabber AT2's 255/65/17
1" Addco rear sway bar
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