Jump to content

Rough Idle Problem


Recommended Posts

We have a 90 MJ with the 4L I6 and 5 spd MT. We had a bit of a rough idle and an occasional backfire so I did what I thought would be the simple fix:

- changed all the plugs (used Bosch quad platinums)

- changed plug wires (napa gold set)

- changed air filter (fram airhog)

- repaired crank case ventalation system leak

 

The backfiring seems to have gone away but I still have a rough idle. Do I need to work on the distributor? Maybe the points are worn? Any suggestions? I have seen some posts about changing out the injectors too.

 

Any help would be most appreciated.

 

Thanks

Link to comment
Share on other sites

When I was given my MJ (for free from a coworker) I replaced the MAP sensor tube (Mopar #53004589). It had an idle issue that he couldn't resolve. I also had a few vacuum leaks that I needed to fix. I used shrink tubing after aligning them together. The vacuum leaks fixed my Vent/ defroster operation. Another would be the IAC (Idle Air Control solenoid on the TB.

Link to comment
Share on other sites

I have not cleaned the throttle body area yet so I will take that up too.

 

To answer Jim's question, the rough idle seems to be more pronounced once the engine is warmed up.

 

Current plan - clean TB, test O2, test MAP, examine vacuum lines. Any other things I should try?

 

thanks

Link to comment
Share on other sites

Have you cleaned the throttle body area? Make sure you use a cleaner that says it's safe for throttle bodies. Pure carb cleaner can wreck havoc on the 02 sensor.

 

Would it be safe to use if the TB was removed and completely wiped down/dried before reinstallation?

Link to comment
Share on other sites

If none of that works, maybe some new Injectors. or take the time to remove, clean and rebuild yours. the ones at the parts store a WAY expensive.

But many of us on here have picked up the ones from BLHATZ and mine did a WORLD of good the way the truck idles!! They cost a bit over 100 clams for a set of 6. That's WAY better than the $40 something EACH at the parts store!!! :eek: :eek: :eek:

 

CW

Link to comment
Share on other sites

Have you cleaned the throttle body area? Make sure you use a cleaner that says it's safe for throttle bodies. Pure carb cleaner can wreck havoc on the 02 sensor.

 

Would it be safe to use if the TB was removed and completely wiped down/dried before reinstallation?

 

 

I would imagine that'd be fine.

Link to comment
Share on other sites

And........if all the above suggestions don't help, check the EGR valve -

 

http://home.sprynet.com/~dale02/egrvalve.htm

 

A bad EGR valve can cause rough idling. Just removing the vacuum line and plugging it will do a quick check for ya.

OOH yea, GOOD catch!!

 

Mine had this issue... solved it temporarily with a golf tee!! At the DS fender stuck a tee in the vac line and go home to swap it out!!

 

Mine was so bad truck wouldn't even idle!!!

 

CW

Link to comment
Share on other sites

Thanks for all the great suggestions. I will follow all of them up since the miss/hesitation came back today :headpop: . What a pain in the butt. I am wondering about the TB now more since it seems to miss or have a hesitation shutter at one specific throttle position. Since I tend to baby my cars and shift early I wonder if this may be more of the problem than I thought.

 

Have plenty of time though since this will be my son's truck and he is a few years away still and it is our father-son project. That being said, I have been driving it and using it since it is way cooler than my normal vechicle (Honda Odyssey minivan) 8)

 

Now if I could get it to run well and if I can find someplace to do a little novice 4 wheeling I would be in great shape.

 

:cheers:

Link to comment
Share on other sites

Well I thought I would post an update on what we did:

 

1. Installed new (rebuilt) injectors from Ford Mustang 5.0L I bought on E-bay. In the process of changing the injectors, discovered a fuel rail leak and two badly messed up injectors. Looks like we averted a fire waiting to happen.

 

2. Installed new fuel filter

 

3. Tested MAP sensor - fine

 

4. Tested O2 sensor - fine (but really rusted up so am going to replace before a problem comes up)

 

5. Fixed the vacuum system. The nitwit who owned the MJ previously had:

- the vacuum line to the Dana 30 shift moter was connected to the MAP instead of the vacuum fitting on by the throttle body

- the throttle body was connected to the vacuum fitting near the throttle body instead of to the MAP sensor

- the vacuum motor was connected to the EGR solenoid instead of the bi-metal temperature sensor

- the other connection to the bi-metal temperature sensor was not connected

-- frankly I am amazed the thing ran at all

 

Drive test - no miss/hesitation and no back firing (so far).

 

Any other things I should worry about?

 

Thanks to everyone who posted suggestions.

 

Now working on leaky exhaust (corrosion), dead parking brake (corrosion), slight lift package, and reinforcing the frame with steel channels (some corrosion), rocker panels (gone from corrosion), and rock rails.

 

I recall someone had a post with a sign that stated something to the effect of spending way too much time and money on upgrades .... we seem to have fallen into this trap but are having fun doing it.

jamminz.gif

Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...