Engine idle fluctuation - Jeep Wrangler Forum
Jeep Wrangler Forum

Go Back   Jeep Wrangler Forum > TJ Jeep Wrangler Forum > TJ Tech Forum

Join Wrangler Forum Today


Reply
 
Thread Tools

Please support our sponsors and let them know you heard about them on WranglerForum.com
Old 03-07-2012, 06:07 PM   #1
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
Engine idle fluctuation

Last night I notice that I had no control over where my heater and air conditioner were flowing air. After a brief search of the web I found that my heater diverter vacuum connection had become disconnected at the intake manifold like is shown here'

All settings on heater/ac/fan blow only through Defroster - JeepForum.com

So I reconnected making one smal change to make the elbow fit tightly into the hose that attaches to the manifold and it works like a charm.

However on my way to work this am I notice that my idle fluctuated between about 500 and 1200 rpm making the TJ almost lurch forward. It only did it in drive after warming up and if I shifted to neutral the idle settled.

Anyone have any thoughts. I went out for some light wheelin this weekend and it was likely disconnect the entire time so I don't know if I sucked dirt into the intake through the open port. There are no other apparent vacuum leaks and other than this lurching, the jeep runs great. Thoughts???

__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Old 03-07-2012, 08:40 PM   #2
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
I did a little more diagnosing

The problem occurs when you just lightly touch the accelerator so as to inch forward and then release the accelerator (like you would do at a backed up 4 way stop sign). The idle drops just below the 1st tick mark on the speedometer (2-300 rpm) and the engine must think its dying so the throttle sensor bumps it up, which pushes the rpm to about 1200 rpm, thus the lurch forward (and you have to be quick on the brake). Its repeatable in any forward gear, but in reverse, removing your foot from the brake is enough to cause the jeep to move. In drive, you do have to press the accel to move forward.

When I disconnect the vacuum diaphragm causing a vacuum leak, the problem goes away. I guess that's why the diaphragm was in loosely when I bought the LJ. It allows the heater control to work but also allows enough leak so that the idle doesn't fluctuate.

Idle is smoother without the vacuum leak, but still smooth with it (a mild stumble). I got 16 mpg with the vacuum leak so its not exactly wrecking mileage. Also I had ok power.

__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Old 03-08-2012, 08:29 AM   #3
Jeeper
 
Join Date: Jan 2012
Location: Suffolk, Va
Posts: 23
Did you disconnect the battery for an extended period of time?
johnnyleo11 is offline   Quote Quick Reply
Old 03-08-2012, 01:31 PM   #4
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
Id id disconnect it a couple of weeks ago after getting a code from some E3 sparkplugs. I changed plugs to double platinum, disconnected and shorted out positive lead for 30 sec. Hooked everything back up and it ran fine...until I had this issue with the vacuum line. I've done a little more diagnosing this morning.

It only does this when the engine is warm and at a stop.

I'm going to clean the throttle body this weekend, and break out the code reader to see if it says anything but Im at a loss why the engine would operate smoother at idle with a vacuum leak than without. Are you suggesting that I do another adaptive memory clear?
__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Old 03-08-2012, 02:44 PM   #5
Jeeper
 
Kimball2's Avatar
 
Join Date: Mar 2012
Location: Sikeston Mo.
Posts: 35
What do u mean by shorting out the possitive lead, how is this done and why/ im assuming to reset comp? how do u short out? i might need to try this on mine Thanks.
Kimball2 is offline   Quote Quick Reply
Old 03-08-2012, 04:03 PM   #6
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
Kimball,
Pull the positive lead off of the battery and touch it to the ground post for 30 sec. That's what I did to make the cel get reset. There's a whole procedure for resetting adaptive memory found here in post #11:

Project TJ Kompressor - JeepBBS

I didn't do the lights thing in that post as its just extra insurance to drain the PCM capacitors.

I saw an improvement in my jeep's performance.
__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Old 03-08-2012, 04:12 PM   #7
Jeeper
 
shrekfx's Avatar
 
Join Date: May 2011
Posts: 197
I had the same issue after my battery died one night and got a jump, the idle was horible. But I disconnected the battery overnight and it fixed everything.
shrekfx is offline   Quote Quick Reply
Old 03-08-2012, 04:47 PM   #8
Jeeper
 
Kimball2's Avatar
 
Join Date: Mar 2012
Location: Sikeston Mo.
Posts: 35
Great1 Thanks guys, seemed like all my problems started after i washed under the hood one day?
Kimball2 is offline   Quote Quick Reply
Old 03-08-2012, 04:56 PM   #9
Jeeper
 
Kimball2's Avatar
 
Join Date: Mar 2012
Location: Sikeston Mo.
Posts: 35
A local mechanic pluged in to my computer and it wouldnt respond at all,i took it to anothe mechanic and no responce,all fuses and such were checked up to the computer and they said were good, their saying the comp. is no good, any suggestions, im still going to reset it, might not do any good But!
Kimball2 is offline   Quote Quick Reply
Old 03-09-2012, 09:10 AM   #10
Jeeper
 
Join Date: Jan 2012
Location: Suffolk, Va
Posts: 23
Kimball2,

Check all of your grounding straps.
johnnyleo11 is offline   Quote Quick Reply
Old 03-11-2012, 12:22 AM   #11
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
Got the code reader out...no codes. Cleaned the throttle body with a can of CRC TB cleaner. Seems to have solved the idle fluctuation problem. So I guess problem solved.
__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Old 05-06-2013, 12:29 PM   #12
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
Hate to bring up an old thread, but I had the exact same thing happen again. It was 99 degrees this weekend and when my wife and kid came home from driving lessons they mentioned that there was no control over which ducts the ac came out. I looked under the hood and is was at the same vacuum connection as March 2012. This time I noticed the rubber was really hot (almost felt moist). Nonetheless, I reconnected the vacuum line using some new rubber hose and that solve the ducting problem. However on my way to work today, the throttle jump was back and worse than in March 2012. When inching along in traffic there were several instances where the jeep lurched forward (rpms on deceleration went from 800 to 300 and then jumped to 1200 all in about a couple of seconds). I thought the problem was that I had a dirty TB last time but this time, I doubt that. Someone suggested that resetting the computer would solve the issue. Can anyone tell me why?

Prior to this, I've been driving the Jeep nearly daily and without event. The vacuum line was connected and performance was good. I find it hard to believe that one day of a vac line being disconnected would throw things that far out of whack. Also, with regard to the rubber vacuum line being almost moist, the engine was quite warm (just above the half way mark on the temp gage in the jeep) and the intake manifold was also very warm. Any suggestions on replacing the vacuum line with silicon lines? Right now I'm just using some old (but unused) fuel hose I had laying around the garage. I'm gonna try to look at this tonite after work although its 59 degrees today (yep 40 degrees cooler than Saturday) and raining so I'm not sure the weather is going to cooperate. Thanks
__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Old 05-07-2013, 10:55 AM   #13
Supporting Member

WF Supporting Member
 
dezertdirt's Avatar
 
Join Date: Nov 2011
Location: La Crescenta, CA
Posts: 56
Well I reset the PCM and it worked. The fluctuation was gone this AM. I don't know why one day with the vacuum line disconnected completely disrupts more and a year of PCM operating properly, but it does...and resetting the PCM fixes all that.

__________________
2005 Unlimited Rubicon, 2.5" OME, JKS UCAs & LCAs, Currie AntiRock
2008 Dodge 3500 4x4
67 Baja Bug
dezertdirt is offline   Quote Quick Reply
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the Jeep Wrangler Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
If you do not want to register, fill this field only and the name will be used as user name for your post.
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:

Log-in

Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.



Thread Tools

Posting Rules
You may post new threads
You may post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Need Engine Help... AbsoluteCats Kentucky Jeep Forum 2 07-10-2012 01:56 AM
New member w/engine issues jimmy86freedom TJ General Discussion Forum 15 03-23-2012 12:40 AM
Jeep Engine swap question brown.jasonc TJ General Discussion Forum 6 03-08-2012 03:21 PM
95 yj 2.5 engine squeal jords toy YJ Tech Forum 4 03-07-2012 09:17 AM
Engine Swap question illf8ed TJ General Discussion Forum 0 03-06-2012 08:22 PM


logo carid shop wrangler parts carid fender flares custom wheels store avs deflectors at carid
» Rates
Get low rates on auto insurance in Canada!

» Network Links
»Jeep Parts
» Featured Product

All times are GMT -5. The time now is 04:36 PM.



Jeep®, Wrangler, Liberty, Wagoneer, Cherokee, and Grand Cherokee are copyrighted and trademarked to Chrysler Motors LLC.
Wranglerforum.com is not in any way associated with the Chrysler Motors LLC