Rough idle on 88 3.9 - Dodge Durango Forum and Dodge Dakota Forums
Register Home Forum Extras Website Features Timeslips Calendar Garage Auto Loans Search Today's Posts Mark Forums Read

2.5L/3.7L/3.9L Engines Questions regarding the I4 and V6 Engines is the premier Dodge Dakota Forum on the internet. Registered Users do not see the above ads.
Thread Tools Rate Thread Display Modes
Old 07-25-2010, 07:23 PM
65CrewCabPW 65CrewCabPW is offline
Registered User
Join Date: Jul 2010
Location: Milton Freewater, OR
Vehicle: 65W200, 93 D250, 88 Dak
Posts: 5
Reputation: 11 65CrewCabPW is just getting started
Rough idle on 88 3.9

I bought this thing as "scrap" from a dealer, and so far I've gotten it mostly good running, but one last thing eludes me. It idles rough. Previous to me, I have been able to see that a set of wires, plugs, dist cap, rotor, fuel filter were all put on, and yet the dealership could not get it to run.

I had to move the timing many degrees (probably around 20-30) to get it to start. Just lining up the 0 mark and locating my finger at the #1 plug spot on the dist cap showed the rotor pointing nowhere near it.

The truck is now responsive, has good power, and seems to not suck much gas, but it idles rough. As in, it has some random misfires at idle. In gear, the truck has an uneven sort of shiver, and when not in gear, you can feel the "putt" out the exhaust when it misfires. It's not steady, and not always the same cylinder.

I don't have any reason to think it has low compression, the plugs are good (new), I've run Marvel Mystery Oil through the gas, which improved things a lot. I replaced the rotor, as the previous "mechanic wannabe" damaged it. Still, no change, really. When you start it cold, it fires up and is smooth until it slows down to normal idle speed, and then it slowly gets "rough". I took it out and did a hard run up the mountains (to over a mile high pass) and back and it's somewhat better, but still has this shivery idle.

Is that by chance normal for a 3.9 TBI? I know old 2.2 and 2.5 Mopars would NEVER idle fully smooth.

Also, is there anything you have to do to set the timing? Wires to remove, plugs to plug, etc?

BTW, I changed plugs to NGK V-Power, changed the O2 sensor as it wasn't working right, and other minor fixes. Still has the uneven hot idle.
Reply With Quote Quick reply to this message
Sponsored Links

Quick Reply

Register Now

In order to be able to post messages on the Dodge Durango Forum and Dodge Dakota Forums 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 email 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
Display Modes Rate This Thread
Rate This Thread:

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

Forum Jump

All times are GMT +1. The time now is 04:44 AM.

Powered by vBulletin® Copyright ©2000 - 2014, Jelsoft Enterprises Ltd.
Garage Plus vBulletin Plugins by Drive Thru Online, Inc.
Copyright 2001-2010 Dakota-Durango Archive