97 TJ hesitation/bucking/stutter/rough idle/backfire on initial start up - JeepForum.com
Search  
Sign Up   Today's Posts
User: Pass: Remember?
Advertise Here
Jeep Home Jeep Forum Jeep Classifieds Jeep Registry JeepSpace Jeep Reviews Jeep Gallery Jeep Clubs Jeep Groups Jeep Videos Jeep Events Jeep Articles
Go Back JeepForum.com > Models > Jeep Wrangler Forums > TJ Wrangler Technical Forum > 97 TJ hesitation/bucking/stutter/rough idle/backfire on initial start up

Engo LED Flush Mount Lights *PAIR* Flood or Spot 1,600 LumYukon Ultimate 35 axle kit for c/clip axles with Yukon ZipRockridge 4WD IS Taking Zone Offroad Suspension Lift Kits

Reply
Unread 08-23-2007, 10:53 PM   #1
zer0321
Registered User
2008 JK Wrangler 
 
Join Date: Oct 2005
Location: SW Washington
Posts: 30
97 TJ hesitation/bucking/stutter/rough idle/backfire on initial start up

I've got a 97 TJ with the 2.5L and 5-spd.

It has a funky issue that only occurs right after the engine has been started (warm or cold, it doesn't matter). 150k on the odometer. No Codes are stored.

After starting the engine, the rpm's drop and almost kill the engine. This can be remedied by pressing the gas pedal enough to keep it from stalling out.

If you try to drive the Jeep normally, as soon as you take off the engine starts to hesitate and sputter while backfiring through the intake, which makes a loud pop noise, which continues until you let off the gas.

The only way this can be avoided is to rev the engine past 3k rpms in neutral and then put it into gear and then gradually let out the clutch.

After this has happened once, the Jeep runs pretty well and does not have the issue anymore until the next time it is restarted. Although it does not seem to be misfiring at this point, The only symptom that remains is a very small bounce on the tachometer needle at idle.

This problem is really annoying me, I cannot let anyone drive my Jeep because they don't know how to handle this situation when it occurs.

What is causing this problem?

I've already replaced the plugs, wires, distributor cap+rotor, and air filter...I replaced the front O2 sensor too, I have looked vacuum leaks, and swapped CPS/TPS sensors as well-

None have remedied this issue...Please Help!

__________________
Black 2008 Jeep Wrangler X Unlimited - Hardtop, Auto, 3.73s, Tow package, Factory Electronic Sway Bar & Rear Locker...
zer0321 is offline   Reply With Quote Quick reply to this message
Unread 08-24-2007, 08:22 AM   #2
Piratejonh
Registered User
1997 TJ Wrangler 
 
Join Date: Sep 2006
Location: SW Florida
Posts: 662
I had the same problem, took me a year to figure out it was the upstream O2 sensor. replaced almost every sensor. Replaced O2 and no more problem. Unfortunately, any of your sensors could be acting up. Do the free stuff first... Gas cap closed and not broke, no vacuum leaks, no cracked header, rotor/cap/plug wires OK, throttle body clean, Idle speed motor clean etc. GOOOOOD Luck!
__________________
Jeep took another piece of my finger today...
Piratejonh is offline   Reply With Quote Quick reply to this message
Unread 08-24-2007, 08:35 AM   #3
ElCanon
Registered User
1997 TJ Wrangler 
 
Join Date: Jun 2005
Location: Boston MA
Posts: 41
Hmmm. You said you replaced the O2 sensors? I had very similar issues with my TJ, same year at roughly the same mileage. I replaced both oxygen sensors and the coolant temperature sensor (it regulates the PCM based on coolant temp - it's cheap and I replaced it based on advice I'd heard here), replaced the cap, plugs, and wires, and it solved my rough start and idle problems. The engine runs awesome now. It seems like misinformation from bad sensors was causing the PCM to go haywire especially before the 2.5L warmed up.

Coincidentally, my sensors never threw a MIL (check engine light) code. I confirmed it by looking at the codes on the odometer using the three key turn trick, which simply showed "55" indicating no stored problem codes. Some here have said sensors can run crappy in a TJ a very long time before throwing a code, and based on my experience, that's definitely true. (As it turns out, I discovered around this time that my check engine light didn't even have a bulb in it, so I wouldn't have discovered a code unless the jeep failed inspection. I bought the jeep brand new so I don't know why the bulb was missing.)
ElCanon is offline   Reply With Quote Quick reply to this message
Unread 08-24-2007, 08:59 AM   #4
jgorm
Web Wheeler
2006 LJ Wrangler 
 
Join Date: Aug 2007
Location: San Diego
Posts: 2,355
Most cars do not use the O2 sensors for the first minute or so after start up. This is to allow them to heat up and work properly. Do you have a CAI on it? My guess is that the MAF is reading wrong. (are these jeeps maf based?) You can clean it with electrical or maf cleaner. After a minute or so it will switch to closed loop and base fueling off the O2 sensors instead of the maf. Going WOT will switch back to open loop. I would also double check the timing considering the backfires. It would have to be one hell of a vacuum leak to cause these issues so you would hear it for sure and it wouldn't go away after driving for a bit. The IAC valve is another possible cause of issues (sometimes they heat up and work better), but i would concentrate on the MAF and the timing. (sorry if I'm wrong, I'm a mustang ECU tuner and just got into jeeps so i'm not familiar with their strategies)
jgorm is offline   Reply With Quote Quick reply to this message
Unread 04-29-2011, 06:46 AM   #5
justicemikes
Registered User
1997 TJ Wrangler 
 
Join Date: Apr 2011
Location: Birmingham, AL
Posts: 5
I'm having the exact same problem. Looks like I have a better starting place now! So far I have changed all plugs and wires, installed new manifold and gaskets, Cleaned fuel systems, no luck with these except for the exhaust leak being fixed. Thanks for your help!
justicemikes is offline   Reply With Quote Quick reply to this message
Unread 04-29-2011, 11:52 AM   #6
Jonny Jeep
Web Wheeler
 
Jonny Jeep's Avatar
1997 TJ Wrangler 
 
Join Date: Feb 2007
Location: Manchester, UK
Posts: 4,729
TJs don't use the O2 sensors immediately so if the issue is right off the bat it isn't O2 related.

How old is the battery? Bad batteries can cause idling problems just after starting. First remove the clamps from the battery, then clean the battery clamps and the battery terminals. Bad connections can create similar problems. If the problem still persists charge the battery up and get it properly load tested at an auto store. If it's bad replace it.
__________________
"Giving English to an American is like giving sex to a child. He knows it's important but he doesn't know what to do with it."
Adam Cooper (19th century)

Rockauto 5% discount code can be found here... http://www.markviii.org/LOD2/products_services.htm

Online factory service manuals (FSMs) and parts lists can be viewed at http://www.jeep4x4center.com/knowledge-base/index.htm
If the link doesn't work properly, look for the service manual link under Jeep Resources at the bottom of the page.
Jonny Jeep is offline   Reply With Quote Quick reply to this message
Unread 04-29-2011, 12:25 PM   #7
rlkelley
Registered User
1999 TJ Wrangler 
 
Join Date: Mar 2011
Location: , Texas
Posts: 146
put some "seafoam" in your fuel.....that stuff fixes everything.. (not really, but its worth a shot)

sounds dumb but that stuff has increased the performance of my jeep, truck, and riding lawnmower !
rlkelley is offline   Reply With Quote Quick reply to this message
Unread 04-29-2011, 02:38 PM   #8
Simpleman50
Registered User
1997 TJ Wrangler 
 
Join Date: May 2007
Location: Myrtle Beach, SC
Posts: 13
I had the same problem. It got to where mine didn't even want to start. I took the throttle body off and cleaned it up real good with throttle body/carb cleaner. There is a good detailed write-up somewhere. I had what looked like chunks of carbon build-up coming out of mine. I replaced the TPS as well. Now it runs like a champ.
Simpleman50 is offline   Reply With Quote Quick reply to this message
Unread 04-30-2011, 09:05 AM   #9
justicemikes
Registered User
1997 TJ Wrangler 
 
Join Date: Apr 2011
Location: Birmingham, AL
Posts: 5
My battery is pretty new and ive checked those connections. I will look at the other sensor and the throttle body to start with. thanks guys for the suggestions.
justicemikes is offline   Reply With Quote Quick reply to this message
Unread 12-22-2011, 11:53 AM   #10
tnovak
Registered User
1997 TJ Wrangler 
 
Join Date: Jun 2008
Location: Greenville, SC
Posts: 5
Having the exact same issue on the exact same car/engine/transmission/year as zer0321.
Did anybody resolve this issue? My plugs, wires, and O2 sensors are all new.
On a possibly related note (but probably unrelated), there is an antifreeze leak from the radiator which is causing some overheating.

Thanks in advance!
tnovak is offline   Reply With Quote Quick reply to this message
Unread 04-30-2012, 02:31 PM   #11
justicemikes
Registered User
1997 TJ Wrangler 
 
Join Date: Apr 2011
Location: Birmingham, AL
Posts: 5
A lot of my issue actually ended up being a hidden crack in my manifold. I replaced it, wires, plugs, and both o2's.
justicemikes is offline   Reply With Quote Quick reply to this message
Unread 04-30-2012, 04:28 PM   #12
tnovak
Registered User
1997 TJ Wrangler 
 
Join Date: Jun 2008
Location: Greenville, SC
Posts: 5
Mine turned out to be the distributor.
tnovak is offline   Reply With Quote Quick reply to this message
Unread 12-14-2013, 04:58 PM   #13
zer0123
Guest
 
Posts: n/a
I have the same problem

What was your solution? I've done everything and took it a step further today and replaced the cat and exhaust. Drove great for 20 mins then, the same damn thing starts happening again. I've given up!
  Reply With Quote Quick reply to this message
Unread 12-14-2013, 05:01 PM   #14
zer0123
Registered User
1997 TJ Wrangler 
 
Join Date: Dec 2013
Posts: 1
I have the same problem

What was your solution? I've done everything and took it a step further today and replaced the cat and exhaust. Drove great for 20 mins then, the same damn thing starts happening again. I've given up!
zer0123 is offline   Reply With Quote Quick reply to this message
Unread 12-15-2013, 06:40 AM   #15
noise_maker
Registered User
2000 TJ Wrangler 
 
Join Date: Nov 2007
Location: Jackson, MI
Posts: 526
It could very well just be the IAC.
Sometimes you can get away with cleaning them to get a little extra life but generally you gotta replace it.
noise_maker is offline   Reply With Quote Quick reply to this message
Reply

Quick Reply
Message:
Options

Register Now

In order to be able to post messages on the JeepForum.com forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.
User Name:
Password
Please enter a password for your user account. Note that passwords are case-sensitive.
Password:
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.
Note: All free e-mails have been banned due to mis-use. (Yahoo, Gmail, Hotmail, etc.)
Don't have a non-free e-mail address? Click here for a solution: Manual Account Creation
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


Suggested Threads





Jeep, Wrangler, Cherokee, Grand Cherokee, and other models are copyrighted and trademarked to Jeep/Chrysler Corporation. JeepForum.com is not in any way associated with Jeep or the Chrysler Corp.