Gen 2.5 Montero rough idle only when in drive. (auction find)

[snakeyjake]

I took a leap and bought a very clean looking gen 2.5 1998 Montero at an online auction out of CA. I was expecting the worst but thus far have been really surprised. The body is nearly perfect and despite the last owner neglecting it the interior is close to perfect as well. I ran a carfax and it was a one owner for the first 20 years and 234k of 243k miles. 2nd owner sort of abandoned it I guess. When it arrived on truck I put in a new battery, changed fluids and it fired right up. Turn signal does not work so I ordered another stem and ordered rear window regulator as one window is non functional. Here is my issue. I think I reset the computer idle properly and the rig idles perfectly in park or neutral but gets a bit rough in drive or reverse. It has not stalled and it does not backfire or throw any codes. Just a bit of rough idle. I have read the forum posts, removed the air idle control and it looked ok, as did the throttle body. I am not mechanically inclined however. Can anyone offer a little advice as to what I should do next? Prefer to sort this out myself if possible before taking to mechanic.

 

[Salonika]

What do you mean when you say you reset the computer idle?

 

[snakeyjake]

I had a 2003 sport. When the battery was changed it started a crazy rough idle and would barely run. I took it to my mechanic and he said mitsubishi's needed to go thru a process where the idle was re-learned? I looked up on another mitsubishi forum and went thru the prescribed process with this one. Idle is still not perfect though. Still rough when engaged in rev or in drive at low rpm. I don't remember it idling smoothly before battery was changed however. This montero has many more miles and it could be a completely different issue. I'm trying to go thru process of elimination to see what could be causing the issue. It's a bit tough when I only have service history from carfax, not previous owners. Will post photo's soon.

 

[PacS14]

Drive it around for a while, I have a 99 and that happens every time I disconnect the battery for a while, it might die at a stop light if you have the AC on, it'll go away eventually

 

[Salonika]

You are correct about the idle relearn procedure, it requires a scan tool capability that most people don’t own. You can get it close without doing this, but probably never perfect like when it was new. I rebuilt my throttle body a few years ago and when I had everything all back together, my local dealer did this for me. It would not idle right until this was done. It’s perfect now and has been ever since. With the scan tool they can actually control the idle air motor and hold it at a certain % open in order to properly set the bypass screws.
Have you thoroughly cleaned all the passages? I’d recommend replacing every single gasket and seal in it before bothering to have the dealer recalibrate it.

 

[snakeyjake]

I have not. I assume you mean removing throttle body and cleaning both sides? I have not done this. I figured with my experience it may be above my pay grade. Is this scan tool something exclusive to a dealer or something my mechanic shop most likely has?

 

[snakeyjake]

You are correct about the idle relearn procedure, it requires a scan tool capability that most people don’t own. You can get it close without doing this, but probably never perfect like when it was new. I rebuilt my throttle body a few years ago and when I had everything all back together, my local dealer did this for me. It would not idle right until this was done. It’s perfect now and has been ever since. With the scan tool they can actually control the idle air motor and hold it at a certain % open in order to properly set the bypass screws.
Have you thoroughly cleaned all the passages? I’d recommend replacing every single gasket and seal in it before bothering to have the dealer recalibrate it.

I'm also going to run some good fuel system cleaner thru it and see if that helps. The car has been sitting around for over a year by my estimation.

 

[Mozo]

Yep..cleaner and put some quality fuel in it..look for places where air may be sneaking into your intake.

 

[nwoods]

Also kinda of sounds like a leaky vacuum line.

 

[Salonika]

I’d guess that many shops could do it, but I had it done at the dealer and I gave them the procedure reference from the FSM. I probably have a few threads on here talking about this, do a search.
The throttle body has a few very small diameter passages that need to be cleaned, not just the main big one, and it’s way easier to do with it removed from truck since there’s so many small parts to deal with.

 

[snakeyjake]

I’d guess that many shops could do it, but I had it done at the dealer and I gave them the procedure reference from the FSM. I probably have a few threads on here talking about this, do a search.
The throttle body has a few very small diameter passages that need to be cleaned, not just the main big one, and it’s way easier to do with it removed from truck since there’s so many small parts to deal with.

Ok I'll give that a shot and report back. Thanks for the input.

 

[snakeyjake]

So the day was going too well. Replaced the turn signal stalk and turn signals fully functional. Replaced Right rear window regulator....fully functional as well. I started and warmed up and ran really well but then suddenly check engine light came on. Pulled code P0431 Catalyst Effieciency Below Threshold. I've been suspecting an exhaust leak because of the smell at start up. If the cat is mostly toast is this something I can change out myself? Has anyone pulled this code before.