99 4.0 bucks at 70 mph, also occasionally dies at idle - JeepForum.com
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 > General Technical Discussions > Engines & Drivetrain > 99 4.0 bucks at 70 mph, also occasionally dies at idle

Income tax season is upon us. We got what u needGet 5% Back On Rugged Ridge-Omix-ADA-Alloy at ExtremeTerraGibson Exhaust Rebate - ExtremeTerrain!

Unread 08-28-2013, 02:10 AM   #1
Registered User
1999 WJ 
Join Date: Feb 2012
Location: Miami, Florida
Posts: 26
99 4.0 bucks at 70 mph, also occasionally dies at idle

Alright this is the GFs Jeep. 99 WJ 4.0 Laredo 4x4 with 185k miles. It was not very well maintained until I met her. Since then I have kept up with the usual crap. We always run decent gas (Chevron or Shell), 50/50 mix syn/dino rotella+pure one filters, k&n filter. I swapped the tranny last year (which has been great) and have done numerous other things since. It seems this is one issue that won't go away, it has has codes in the past (o2, evap, map, i believe it once had a code for coils) but it currently has no CEL/codes.

Related things i've fixed:
Rebuilt fuel pump/cleaned tank, new gas cap
changed fuel filter
gently cleaned injectors to the best of my ability
fuel pressure checked nice and high after new pump

checked and cleaned all electrical connectors for sensors and what not, fuses, etc
visually checked and replaced/repaired all vacuum hoses (that I could find)

replaced MAP, IAC, TPS, front O2 sensor, plugs, and supposedly either the crank/cam sensor or both were replaced at some point.

Now the problem is that sometimes, on the highway, at about 70mph the car will buck. It used to be a lot worse, now it'll just buck for a moment and carry on. My GF also says that the car will die sometimes at idle when accelerating from a stop light, particularly with the a/c on. At this moment in time i'm thinking possibly replace the cat (gonna check the spark plugs again to see if it's running too rich as well as check to see if there is too little exhaust coming out of the exhaust). Other than that I'm thinking possibly crank/cam sensor, PCM, faulty/dirty injectors or some vacuum that i've missed. I also noticed that if you gun it when it's parked, the exhaust spits a bit of smoke and sprays a bit of what looks like black oil.

Anyway aside from the usual crap like both windshield washer pumps leaking from the same little hole, leaking main seals, a/c only works on high because resistor board totally fried (not sure if there's a way to hot-wire, taking the board out of the equation completely), a/c blows all retarded and mostly at the floor, ****ty MPG, no horn/cruise control, tailgate doesn't lock, brake lights keep going out, exhaust rubbing, random parts breaking every other week, blowouts on test drives, starter failing after fixing some other ****, etc, I just want to fix this one thing so she can be confident driving it until we get something else.

Thanks for the help in advance!

madmanmarz is offline   Reply With Quote Quick reply to this message
Unread 09-06-2013, 10:54 AM   #2
Registered User
Join Date: Feb 2013
Posts: 663
When it bucks does the rpms jump?
Speedymcracer01 is offline   Reply With Quote Quick reply to this message

Quick Reply

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:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid e-mail address for yourself.

Email Address:


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

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.