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Unread 06-30-2013, 05:24 PM   #1
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Low idle surges. Issue explained in full detail.

1996 Zj 4.0 stock with 140,000 miles. I am not throwing any codes. About a year ago my Jeep sat for 7 months. I started it up twice a week give or take during the 7 months. I didn't drive it because I blew gears in my dana 35 ( I don't off road) learned my lesson about changing diff fluid. Finally got around to replacing the rear axle and took it for a drive. Idle was terrible when i'd come to a light. I would slow down and then the idle drops roughly (about 2-3 times) to 200 rpm's then slowly comes back up. Never had this problem before. Doesn't seem to matter if the engine is hot or cold. The idle is 475-500 rpm's in neutral. I've put 1,500 miles on the jeep since i got it running again.

I have an exhaust leak. Located at the end of the down pipe right at the small bend where the catalytic converter is bolted on.

I also notice when i put the windows up or turn power steering full lock, idle drops and lights dim. Could be a totally different issue. Just making sure i covered everything.

So far I have:
Exhaust Manifold
Cleaned PCM connectors. The outside was rusted but the connectors were pretty clean.
New Battery
New Alternator (not rebuilt)
New Ignition Coil
New Battery cable ends
Cleaned the IAC/ complete throttle body, and air intake tube (stock).
New Mopar TPS.
New air filter (paper).
New fuel filter.
New spark plugs (champion copper, proper gaps), wires, rotor.
Seafoamed the jeep to clean it out a bit, through the gas tank and throttle body only. Didn't get any smoke out of the exhaust.
Replaced the Valve cover gasket a year ago. The rocker arms were solid and the inside was clean.
Drained transmission and new transmission filter.
Drained engine coolant through the coolant draincock (not leaking, I got lucky)

I have tried checking for a vacuum leak but I'm not completely sure how well i did. I sprayed all the lines pretty well with starter fluid and didn't notice any surges. Cruise Control works, not sure if that means anything.

Still gets good gas mileage and I use the best of fluids and filters.

Finally gave in and took it to jeep. Jeep guy said they reset the IAC motor (whatever that means.) The jeep tech asked me if i had a new engine in the jeep. Since its not, he said the engine may be going bad and he wasn't sure what the problem was.

Bad PCM? Upstream O2?

I've tried to do my homework to get this fixed.

Any help is very much appreciated! Thanks!

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Unread 06-30-2013, 07:33 PM   #2
HandsOn
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Quote:
Originally Posted by ngould1 View Post
...Jeep guy said they reset the IAC motor (whatever that means.)
Can't help with the actual problem, but can help clear up at least a part of what's been done.
The "IAC" is the Idle Air Control valve. Usually mounted to the throttle body (not sure specifically about your engine, but that's the standard place) and literally lets the computer control all aspects of the idle.
It's basically an electro-mechanical servo motor thingy that the computer varies the opening on, while basically leaving the main butterfly valve of the throttle body alone.
(edit: oops! sorry about that. I see you know what it is, but were just asking about the "reset" bit. Sorry for all the added fluff. Maybe it'll come in handy for someone though!)

By "resetting" I assume they did something with regard to unplugging the battery, re-adjusting any possible mechanical parameters (many don't have any physical adjustment) and maybe even manipulating the throttle through it's complete travel while the computer was relearning to read the electrical values.

Take all that with a grain of salt. It's not based on any deep knowledge of Jeep electronics. Just a basic "enough to get me in trouble" level of knowledge.

Paul
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Unread 06-30-2013, 08:04 PM   #3
Oldfrog
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1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
Posts: 4,030
I'd start with all of your grounding points, because you said:

"...I also notice when i put the windows up or turn power steering full lock, idle drops and lights dim."

Lights that are dimming are a symptom of low ( or unclean) power, naturally.....and it could be caused by the idle dropping. But you said it dropped when you raised the windows....etc....in other words, putting a load on the 12v system....possibly causing the idle to drop. ( which is first? chicken or the egg scenario...)

That can only be 5 things....assuming that's the case.
1. Bad battery
2. Bad connections. ( somewhere)
3. Bad alternator
4. Loose serpentine belt
5. Bad voltage regulator in the PCM, which I doubt....but it's possible.

Ok....6 things.......something else is drawing too much power is also a possibility. Aftermarket audio system, something with a slight ( high resistance) short to ground, etc.

Maybe 7. Do your dash lights work properly ? ( thinking headlight switch assembly here)

Double check all of this stuff....but start with the grounds.
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Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

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Unread 06-30-2013, 09:45 PM   #4
um7267
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1998 ZJ 
 
Join Date: Jan 2013
Location: Grove City, PA
Posts: 404
Quote:
Originally Posted by Oldfrog View Post
I'd start with all of your grounding points, because you said:

"...I also notice when i put the windows up or turn power steering full lock, idle drops and lights dim."

Lights that are dimming are a symptom of low ( or unclean) power, naturally.....and it could be caused by the idle dropping. But you said it dropped when you raised the windows....etc....in other words, putting a load on the 12v system....possibly causing the idle to drop. ( which is first? chicken or the egg scenario...)

That can only be 5 things....assuming that's the case.
1. Bad battery
2. Bad connections. ( somewhere)
3. Bad alternator
4. Loose serpentine belt
5. Bad voltage regulator in the PCM, which I doubt....but it's possible.

Ok....6 things.......something else is drawing too much power is also a possibility. Aftermarket audio system, something with a slight ( high resistance) short to ground, etc.

Maybe 7. Do your dash lights work properly ? ( thinking headlight switch assembly here)

Double check all of this stuff....but start with the grounds.
every car that i have had did that i even replaced the grounds with a kit off ebay in my last car.

here the kit if you want to try it
http://www.ebay.com/itm/6-points-Gro...c751ad&vxp=mtr

i may be replacing mine sometime having short wires for the battery drive me nuts
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2004 Lexus Es330, alive; 1999 Cherokee Sport
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1997 Grand Cherokee; Black and Gold, Limited 4.0....RIP 2005
to the good times and the bad, the family we have and lost, little brother 1988-2011
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Unread 07-01-2013, 11:08 AM   #5
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Quote:
Originally Posted by Oldfrog View Post
I'd start with all of your grounding points, because you said:

"...I also notice when i put the windows up or turn power steering full lock, idle drops and lights dim."

Lights that are dimming are a symptom of low ( or unclean) power, naturally.....and it could be caused by the idle dropping. But you said it dropped when you raised the windows....etc....in other words, putting a load on the 12v system....possibly causing the idle to drop. ( which is first? chicken or the egg scenario...)

That can only be 5 things....assuming that's the case.
1. Bad battery
2. Bad connections. ( somewhere)
3. Bad alternator
4. Loose serpentine belt
5. Bad voltage regulator in the PCM, which I doubt....but it's possible.

Ok....6 things.......something else is drawing too much power is also a possibility. Aftermarket audio system, something with a slight ( high resistance) short to ground, etc.

Maybe 7. Do your dash lights work properly ? ( thinking headlight switch assembly here)

Double check all of this stuff....but start with the grounds.
I'm assuming if there is a bad voltage regulator the PCM will need replaced?

No aftermarket radio. Just the old Infinity Gold system lol.
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Unread 07-01-2013, 11:10 AM   #6
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Quote:
Originally Posted by um7267 View Post
every car that i have had did that i even replaced the grounds with a kit off ebay in my last car.

here the kit if you want to try it
http://www.ebay.com/itm/6-points-Gro...c751ad&vxp=mtr

i may be replacing mine sometime having short wires for the battery drive me nuts
Whats the difficulty of doing this and where do i start? I have not been able to find any write up's on replacing grounds.
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Unread 07-01-2013, 11:12 AM   #7
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
This is exactly what was written on my receipt from jeep about the IAC motor.

"R/R air motor and reset steps showing 24 steps and now at 9, no faults reading ok at target idle 760."

R/R air motor?? I assume the factor idle is 760 rpm's. I'm no where near 760 if that's the case.

I need to learn how to better utilize "quotes" on Jeep Forum..
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Unread 07-01-2013, 02:38 PM   #8
Oldfrog
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I wouldnt place much faith in what the stealership tech guy wrote if he didnt fix the problem in the first place.

You might try pulling the IAC yourself, spraying some throttle body cleaner in there, let it dry, then reinsert it. Check for vacuum leaks too.
__________________
Cajun Recipes and Fishing tips

Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
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Unread 07-02-2013, 03:09 PM   #9
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Okay. So i went to the advance auto parking lot to work on my car. Pulled the map sensor to make sure the vacuum elbow wasn't cracked, looked fine to me. One of the advance guys said hey I'm a big xj guy let me look at it for you. So the car is running and without asking he pulled the wiring harness on the map sensor. Engine shut off which I think is normal. Well now I'm throwing a code 14(didn't realize until I got home). I'm not sure if he broke my map sensor or what. Code 14 is "Fault in the map sensor electrical circuit." Sounds like possible vacuum leak, exhaust manifold or map sensor. I'll be thoroughly checking all 3 this weekend.
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Unread 07-06-2013, 08:30 AM   #10
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Well I checked all 3 possible problems. No vacuum leak. MAP sensor is fine. I do think there is a crack on the manifold. From reading another forum (http://www.jeepforum.com/forum/f13/e...ensor-1545235/) I think the manifold is causing the vacuum leak. As the leak gets worse I am noticing the heat under the hood to be increasing. Thanks everyone for your help!
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Unread 07-06-2013, 06:19 PM   #11
Oldfrog
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1997 ZJ 
 
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Location: Louisiana/Texas
Posts: 4,030
That guy probably now owes you a PCM. Hopefully not...
Geez...NEVER unplug a sensor with the engine running and first disconnecting the battery !

I know you've done a few things to it...but have you REALLY taken a good long look at the battery cables themselves? The stock cable ends suck, you know.
I had to cut mine back and install new clamps. Not much room to work with, there.

Cleaned the PCM ground at the block ? ( below the coil...but disconnect the battery first) How about the ground under the oil dipstick?

And of course, have you removed the throttle body and cleaned it, as well as the IAC itself?
__________________
Cajun Recipes and Fishing tips

Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
Oldfrog is offline   Reply With Quote Quick reply to this message
Unread 07-07-2013, 05:43 PM   #12
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Man, I hope not! PCM is still working (i think), but I still cant believe he did that!

Just replaced the cable ends. The cables themselves were dirty inside so I cleaned them off as best as I could. Makes me think I will have to replace all the grounds. Any diagrams for this?

I replaced the ignition coil. Old coil was cracked through.

I have not checked the PCM ground or the ground under the dipstick. I have no idea where they all go.

I did a complete throttle body and IAC cleaning a few weeks ago.

Now I'm not sure what to replace next.. Pretty soon I'll be a zj expert ha ha.
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Unread 07-07-2013, 06:25 PM   #13
Oldfrog
Web Wheeler
1997 ZJ 
 
Join Date: Feb 2008
Location: Louisiana/Texas
Posts: 4,030
"....I replaced the ignition coil. Old coil was cracked through..."

Bingo. The ground on that coil is where the PCM is grounded, I'm told.
Dont be surprised if the PCM was fried during this process, though.. Especially if you didnt disconnect the battery when you swapped the coil...or you "made and broke" contact several times while disconnecting it.

Hopefully that isnt the case.

As for becoming a ZJ expert, I hear you but I dont think there is such a thing. We are all still learning about these things. If they didnt have such good 4 WD systems or the 4.0 engine, I'd be driving a Yukon....but that's another set of problems all by itself.
__________________
Cajun Recipes and Fishing tips

Words of wisdom, Posted by Zeejay:
"..it's not air, it is the opposite of air... suckage so to speak."

Stalling? Work through Zeejay's list
Oldfrog is offline   Reply With Quote Quick reply to this message
Unread 07-08-2013, 11:14 AM   #14
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
Progress, alright!. Whenever I work on anything like sensors or electrical I unplug the negative battery cable; unlike the guy from advance. So much good information, much appreciated!
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Unread 11-19-2013, 04:39 AM   #15
ngould1
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1996 ZJ 
 
Join Date: Feb 2012
Location: Columbus, OH
Posts: 50
*update*

A few days ago I replaced the exhaust manifold. Nice crack around the collector. Also replace the upstream O2 Sensor. Since the fix, rough idle/surges have gone away. Its amazing how the jeep drives with ease again.
Still have an electrical issue/ power steering pump on its way out. They are next.

Thanks!!
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IAC issue , idle , o2 , pcm , zj

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