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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8612
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Montero Limited: I have a 2003 montero the check

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I have a 2003 montero the check engine light and skid light keep coming on, at the time they come on I experience a loss of power and popping sound in the engine. The engine code are mis fire and each time in a different cylinder.  I have had it in the shop twice now and code show a mis fire but in different cylinders each time. So far I have replaced fuel screener before fuel pump, spark plugs, plus wires and the valve cover seals as it was leaking oil on the plugs. But two days after all that work it happens again. Anyideas?


How long has this been occurring (weeks/miles/etc)?

What faults are being set in the traction system?
Customer: replied 4 years ago.

Been going on for about a month now it has 107k miles on it. When codes are read it doesn't show anything for tractions system just the mis fires. But when it happens I will be driving and seems to lose power for 30 seconds to 2 minutes then runs seems to run fine again. Happens at different speeds and usually on a warm engine after driving for 10+ minutes.

Customer: replied 4 years ago.

I've had it to local shop they are ones that did plugs, wires and valve cover gaskets run me about $700 so far. There isn't an actual Mitsubishi dealer with in 400+ miles so stuck with other dealers or local shops.


Do you know if the shop has a traction/TCL capable scan tool, or are they just doing an OBD scan? A Mitsubishi specific or other high end scan tool is needed to scan the traction system.

When you say it loses power, does the gas pedal become non responsive... like you can step on the gas all the way down and it doesn't make any significant difference from barely applying it (almost as if you aren't giving it gas)? Or when you press on the gas the engine lugs/misfires loudly, strains etc?
Customer: replied 4 years ago.

I don't know about the scanner I will ask when they are open in the morning.


I've noticed that the rpms drop and can hear a popping (almost like pop corn popping) under the hood, there's also a deep bassy sound at the same time. If I give it gas just seems to not do much then after a minute or two it clears up and power is back.


I'm curious if the throttle body might be shutting down here. The 2003-2006 Montero uses an electronic throttle that is incorporated into the traction system. The traction system uses the electronic throttle to cut engine torque on demand, so any malfunction of the throttle will set a traction failure as well.
This is the only reasonable connection I can see there which would cause pretty much zero response from the gas pedal and would turn the traction lights on. An unwanted closing of the throttle would cause random misfires as well resulting in some pops under the hood and a booming sound from the exhaust.

Lets see if they can get that traction system scanned during/after the problem occurs (before the key is shut off) to see what is being reported there... odds are it is going to give a good indication of your issue.
The throttle body is one of the very few things that can cause random widespread and the fuel (quality and pressure) are about it, as everything else can be broken down into individual cylinders (each injector, each cylinder pair for coils, each cylinder for plugs, each bank for O2 sensors etc). A problem with the throttle or fuel source would affect all cylinders randomly which is what it sounds like is one of the symptoms you are seeing.
Beyond the traction system inspection, a fuel pressure test may not be a bad idea too since that also fits in with random misfire issues, but lets stick with what has the most arrows pointing at it for right now.
Customer: replied 4 years ago.

They did say they checked fuel pressure and it was good so I'll check on if they scan traction

Check it out, if the light is coming on there is going to be a reason.... something has to set. Odds are it will be helpful in understanding what is occurring.
Customer: replied 4 years ago.

OK I just ran to auto zone because light popped up again and had them read me the code they could. It shows cylinder 6 mis fire, 2-3 too lean and 1-4 too lean. Codes are p0171, p0174, p0306. Does that change anything?

Yes, a little.

If you are getting too lean codes then we have something more to work with.
Seeing P0171 and P0174 both over ride any misfire codes, as those two codes will cause misfires.

P0171 and P0174 are both indicating there is too much oxygen content in the exhaust on both sides of the engine... meaning they aren't getting enough fuel or are "lean". This goes back to what we were discussing earlier about possible causes for random misfires being basically throttle related or fuel supply related.

If the fuel pressure has been tested and was OK, you have two areas of concern to investigate:
1 - search the vehicle thoroughly for vacuum leaks. Any vacuum leak (gasket, hose, etc) will cause unmetered air to enter the engine resulting in a lean condition
2 - the fuel pressure regulator is common to cause lean conditions on this model (enough so that bulletins have been released on it)

The first is pretty straight forward. The shop can use a can of propane or brake cleaner to spray around the engine while it is running... if there are leaks, it will draw in the added fuel and cause the idle to change. When that happens, repair the area that is drawing in extra air.

The second is a bit more work. Most shops do not have the proper equipment to measure fuel pressure while running (it requires a Mitsubishi only adapter) so they can only test cranking pressure. The regulator however bleeds off pressure after this test point so it can only be tested with the engine running.
If the pressure is tested within range when cranking but when running it drops down (Below 38 psi at idle or below 47 psi with vacuum line disconnected), the fuel pressure regulator will be at fault.

While it is certainly possible to have two O2 sensors fail causing similar behavior, it is extremely unlikely to occur, never mind to occur and not set other problems. With only lean condition faults on both sides and random misfires, and with the fuel pump pressure already tested OK, look in to vacuum leaks first, then fuel pressure regulator operation.
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Customer: replied 4 years ago.

So I also found today a vacuum leak at what I believe is called a throttle actuator, could be wrong on the name. Its a gold round guy that looks like it opens and closes baffle in the intake. Any idea where I can find this part? I've been everywhere in town and no one can find it or even a name for it. My Subaru dealer told me it does come with the complete aluminum intake but that's $850. There's got to be a way to just get the vacuum part it comes off with two screws. Any ideas?


It sounds like you are describing the throttle body/actuator. This is the large part on the end of the intake right before the big rubber hose. Inside has a gold "butterfly" like on a carburetor that opens and closes with pedal application. This is a pricey unit, but is sold separately from the intake.

Is this what you are describing? If so, where exactly is the leak coming from on it?
Customer: replied 4 years ago.

Mine is fuel injected this part is about the size of a chew tobacco can and about an inch thick has a vacuum hose on one end and a rod that moves in/out on other end that connects to I'm guessing a moving baffle inside the intake. the vacuume hose from it runs into the electronic vacuum cylinoid. Its located in the center of plentum intake on front side of engine

Thanks, I was just comparing the inside in appearance to a carburetor, I thought that might help the description.

Your further description helps me more though, I understand now you are referring to the variable air intake control system.... the long shaft that runs through the intake manifold.

Unfortunately this information is correct regarding the manifold (lower) needing to be replaced to get this part. The variable air intake is internal to the manifold and not separately serviceable..... so any failure will require a new manifold if you wanted it replaced with new. While not $800, if you are paying to have it installed you would be in that range.

Is the vacuum leak from the diaphragm, or where the shaft enters the manifold, or?
Customer: replied 4 years ago.

Yes its coming from that diaphragm on the front you can hear it hiss outthe bottom side. And of course it stopped if you unhook the vacuum hose. I might try some local junk yard it comes off with two phillips head screws.


I have had people swap that diaphragm over before (not for leaking, but rather for a broken spring). There is no real harm in doing this, just take the salvage one apart first, then once you get a feel for how it comes off go to yours and remove/replace it in one shot so there is no confusion about orientation if you have to step away etc. It is pretty straight forward though on this model. On earlier ones there was a secondary linkage and it was a bit of a mess getting it apart. On your 03 it should be rather cut and dry though.