How is the idle controlled on a 2003+ (3.8L) Gen3 Monty?

haolepinoy

Incomplete Idiot
What controls the idle speed on a 2003+ (3.8L) Gen3 Monty? Could someone explain to me how it works?

I've had an idle that sits at or slightly below 500 rpm when I'm in Drive sitting at a stop. Seems low to me, like maybe there's a gunked up component in there that needs to be cleaned (I just don't know who it is) or an adjustment that needs to be made. The Haynes manual for the Pajero says normal idle is around 700, slightly higher with the A/C running. I've also had a few instances of stalling when I've got several electrical components on or the a/c (but I think that's a different issue...a whole 'nother thread).

It's my first time dealing with an electronic throttle body so I've searched in vain for a non-existent IAC motor to clean (my first instinct). I've read about ten contradictory idle speed "relearn" procedures for the PCM. There's rumored to be an idle adjustment solenoid that bumps up idle speed when the a/c is on. The previous owner's service records have instances where idle troubles were associated with MIL codes for the MAF sensor (their notes also suggested a failing PCM could cause the idle issues). How does the EGR tie in, or PCV, or any of the other components in the vacuum system? Needless to say, I've been reading across the internet all week trying to sift through solid info versus not-so-educated guesses and am a little more confused than I should admit.

I'm 3 months into Montero ownership and am more than elbow deep into most of the "common" issues (glove box latch, rear seat latch, free-wheel solenoid, cam seal leaks, instrument cluster lights, and on and on...). Seems the previous owner managed to accumulate almost all of them before selling the car to me. It feels like I'm in intensive automotive school (a good thing for my brain, but not the wallet). The learning curve has been steep, so any advice/help from those of you who are more seasoned Mitsubishi owners is very appreciated (my Google skills are getting a little better Jeep-n-Montero, but they're not top-notch yet...spent a solid week there before posting here).

John in VA
 

fernandez32112

New member
2005 Montero Throttle Body Idle Problems

I own a 2005 Montero Limited 3.8l with 88,000 mls and I am having the same exact problems. Engine cuts off at stop, especially when the ac is running. I'm tempted to just spend the money on a new Throttle Body but the part is very expensive. I wanted to know if you were able to verify that in fact it was a bad throttle body that is causing the problem and if you were able to fix it?

Alex in Miami
 

haolepinoy

Incomplete Idiot
I have another thread on here called "A Story about Slaying Electrical Gremlins" that details more of the process I've followed concerning this issue. Long story short it isn't in the throttle body. The previous owner's mechanic replaced that in a jack-legged attempt to fix the problem. There are simple FSM tests for testing the motor and signal that you can do with a basic multimeter (page #s in the other thread). My issue is one of three things: 1) A/C 2 Signal (either bad PCM bus or wire), 2) possible voltage regulator or alternator issue (I doubt this though), or 3) something in transmission fluid or torque converter since the issue only occurs in Drive or Reverse when TC load is engaged (found a long thread about it here: http://www.justanswer.com/mitsubish...o-limited-2004-montero-limited-dies-when.html

I've found a way to manage my issue, basically by keeping the a/c out of max mode (thermostat all the way down and fan all the way on). It rarely stalls with the fan on a lower setting unless I have other accessories on, and even then it is manageable. We just got back from the OBX where it was around 100 degrees and were cool as cucumbers with no issues just as long as the fan was on a lower setting. The A/C 2 Signal is the one responsible for max mode, and A/C 1 Signal is regular a/c and it seems to work just fine.
 

haolepinoy

Incomplete Idiot
I own a 2005 Montero Limited 3.8l with 88,000 mls and I am having the same exact problems. Engine cuts off at stop, especially when the ac is running. I'm tempted to just spend the money on a new Throttle Body but the part is very expensive. I wanted to know if you were able to verify that in fact it was a bad throttle body that is causing the problem and if you were able to fix it?

Alex in Miami
Does your Montero cut off at stop without the a/c running?
 

Offroadmuch

Explorer
Mine does not shut off but the idle is low as you all have described. I have heard the injectors need cleaned or replaced. What about the idle air control valve? Does that effect this?
 

haolepinoy

Incomplete Idiot
There's no IAC on our 3.8L's. That was my first guess, but I searched in vain to find it. Everything is PCM controlled.

Any more details on injectors...what kind of other symptoms would accompany that? Erratic idle, stutters, MIL codes?
 

haolepinoy

Incomplete Idiot
Mine does not shut off but the idle is low as you all have described. I have heard the injectors need cleaned or replaced. What about the idle air control valve? Does that effect this?
If your idle is a little low the FSM's first recommendation is to check and clean the throttle body and intake. Claims that can prevent it from staying at 700 +- 100 rpm. Really simple on ours since there isn't a TPS or IAC motor to disconnect.
 

Offroadmuch

Explorer
haolepinoy -thank you for this.....

"If your idle is a little low the FSM's first recommendation is to check and clean the throttle body and intake. Claims that can prevent it from staying at 700 +- 100 rpm. Really simple on ours since there isn't a TPS or IAC motor to disconnect."
I will try this!
 

fernandez32112

New member
I already cleaned the throttle body. I only have the problem when front ac is on hi, less than 40% no problem. My mechanic feels it a grounding issue and happens when the ac fan is pulling more amps on hi. If I only run the rear a/c hi or low,., I don't have this problem. So wouldn't the rear a/c also pull just as many amps on hi?. I'm going to flush trans and change trans filter, just in case. I really don't think that's the problem.
 

fernandez32112

New member
I'm considering drilling a small hole approx. 1/16" in the throttle body butterfly. This will allow more air when engine is idle so RPM don't dip below 500-600. Any thoughts?
 

fernandez32112

New member
BTW my car is not throwing any codes. No "check engine light" and the transmission is smooth. Can fluctuating voltage from the alternator or battery cause the engine to idle rough?? Bad plugs? I have a computer that reads all live data. How can I use that data to diagnose this problem?
 

122andy

Observer
I wouldn't do that. That would basically be like having an intake manifold gasket leak. The ecu will be trying to adjust and more than likely you would get idle surge.
 

haolepinoy

Incomplete Idiot
I already cleaned the throttle body. I only have the problem when front ac is on hi, less than 40% no problem. My mechanic feels it a grounding issue and happens when the ac fan is pulling more amps on hi. If I only run the rear a/c hi or low,., I don't have this problem. So wouldn't the rear a/c also pull just as many amps on hi?. I'm going to flush trans and change trans filter, just in case. I really don't think that's the problem.
It sounds like it likely might be in the A/C 2 Signal in this case then. The procedure to check is 13Ad-70 in the 2003 Factory Service Manual, though as noted by Super Doug on the justanswer.com thread there is a misprint in the instructions (the vehicle will not start with the D-134 connector disconnected and must therefore be backprobed). I thought about a ground too, but after refreshing all engine bay grounds I noticed no difference. There are several grounds inside the vehicle cab, but I haven't investigated those.
 

122andy

Observer
Try cleaning it too, as mentioned. The correct way to fix would obviously see if there is capability out there to reprogram the ecu. I dont know if a dealer is capable of that or would even do it if requested.
We used to get custom eproms burned for our ECU's that bumped idle for cams, along with all kinds of other tweaks.
 
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