I've got a 2002 Montero XLS, with 168k miles on the clock. I love driving this thing and plan on keeping it for years to come. The issue I'm having is a rough idle and a sporadic miss fire. First code was PO306. I pulled the plenum and installed new wires and plugs. That didn't help. The next code was a right upstream O2 sensor. That didn't fix it. The next code was a Vacuum issue. I changed out the EGR and the EGR vacuum solenoid. Checked the vacuum lines. That didn't fix it. The next code was PO300. A random miss fire. Since I'm at the limits of testing for the tools I have, I've taken the vehicle to a shop. The cylinder head compression test and leak down test showed nothing out of normal. The coolant pressure check is good. The shop has a automotive electronics specialist coming in to help diagnose the issue. I've changed the spark plug gaskets and the valve gaskets because the spark plug gaskets were leaking. I've changed the plenum gasket to. The master tech at the shop isn't coming up with anything and, of course, I have no idea of what's wrong. Any ideas? I'm thinking maybe a computer / ECM. Any idea what one costs?
Thanks.

Also, my indicator for the 4x4 front tires blink now. Kind of odd. The temp gauge has an issue but it has been an issue for a long time. It goes straight to hot when you start it up.
Thanks.

 

Okay, update: the electronics specialist did not fine anything. The shop walked away from it. But I did get a lot of the "could be" issues out of the way, for free. Now, I'm taking the shot gun approach to fixing this. Dumping parts into it. I've changed the vacuum lines, and the ICM. Changing the ICM made a big difference, in that, it runs at highway speeds perfect now. The idle is still very rough. The 4x4 indicator is still flashing. I've run another can of Seafoam through it with premium gas, of course, over the past couple weeks.

 

swap the ignition module from one at a junkyard

i had the same code p0300 and threw parts at it all day long

sympton is cold start fine, warms up rough idle, coil for 3 and 6 dont get spark when the car is warmed up

try that thing, ignition module, its on the left side of the coils on a bracket looking at the engine

 

You might need to replace the IAC.

 

I have the same issues, but looking at what you have done and what I know about mine may bring clarity to both. I was thinking I had a valve or piston issue because there is a light knock/ping and the power isn't right. I can run hwy speed, but acceleration isn't as solid or firm as I think it should be.

What I know is the fuel filler evap lines are rusted out . . . gone. Only the filler neck is complete and it leaks some. I was thinking engine replacement or valve job on the head with the noise, but now I will wait until I get these fuel lines at filler neck replaced. I have codes for one O2 sensor and fuel lean on bank 1 and 2.

 

Few things come to mind:
1 - By any chance did you have a timing belt done before the rough idle/misfires started? If so, the belt can be off by just one tooth and you'll get these symptoms.
2 - dirty throttle body. Remove and clean out with carb cleaner. Make sure all vacuum passages are clear.
3 - vacuum leak and/or malfunctioning MAF
4 - Ignition module problems.
5 - Possible issues with fuel pump (although you are saying it OK at highway speed).

 

HunterD, It was rough and worse when I purchased it. I didn't appear to have had very good maintenance, so I started replacing the timing belt and water pump, plugs, wires, and air filter. I also replace the front passenger camshaft seal which appeared to have recently started leaking. It runs much better, but it still has a heavy slack adjuster noise on the passenger side.

I noticed the throttle body was very dirty when I disconnected the air intake, so I will give that some attention to remove and clean. It runs fairly smooth, but sometimes feels like a little miss under a load (uphill) but the only codes I get are an O2 sensor and fuel mix lean on both banks, which I understood is attributable to the evap lines being open in the back.

Oh, I also replaced the ICM as I read it was common issue on misfires, which I had before the big tune-up. I am getting rear cam oil seals to replace soon because there is a pretty good leak to them.

I read somewhere Mitsu had a service bulletin on the Monty on how to reset the slack adjuster from the knocking because it was a common problem. Someone said overfilled oil, low oil and dirty oil could all cause them to start knocking. After I replace seals, I will do an engine flush, and on refill add some marvel mystery oil to help clean out and better lubricate the slack adjusters.

 

Hello Miduncan96, Are you talking about cleaning out the LASH AJUSTERS here. ????

 

If you are talking about valve lash adjusters, than yes - the do occasionally start making noise. How bad is it? Does the noise go away after awhile or is it constant? There is procedure for bleeding them but it only works if they have an air bubble trapped in them. If lash adjusters are worn or busted, it will not fix it. However, I don't believe having too much slack will cause any symptoms other than ticking noise. If you PM me your e-mail address, i can send you a PDF page with lash adjuster bleed procedure. But let me emphasize - lash adjusters would not cause rough idle, just less than stellar noise level.

Now back to the codes. Can you post the actual freeze frame data for the current code(s). Without that we are just guessing blindly. You say you have an Evap system leak. It is possible that your vacuum leak is so enormous that computer is unable to dump enough fuel to maintain optimal running. If this is the case, it can cause random misfires. Vacuum leak may possibly explain the rough idle especially that you say it runs OK at highway speed (at full throttle vacuum leaks are very negligible).

Can you get to the bad/corroded hoses from the evap system? Is it possible to pinch off a rubber hose part that goes to it and see if it will stop the vacuum leak?

 

My apologies. I did mean lash adjusters. I had found and printed off the service bulletin on adjusting or resetting them. I tried before doing the timing belt and all and it wasn't working. I noticed today, after adding 3/4 quart of oil, that the ticking had disappeared. It runs quiet and smooth at idle now.

I don't know about a freeze frame. I will try to get the exact codes and some relevant data tomorrow. I use a Bluetooth OBD that works with my android phone with the Torque app.

I did notice that my coolant has gone from bright green to very dark. It was almost black before the water pump replacement and is approaching that again. I tried to research what would cause this and didn't find a lot. It was not mixing cooling types. It is not oil in the coolant. I thought previously someone had put some kind of sealer in the coolant. From my research, I am thinking it could be the hoses breaking down internally and polluting the fluid.

My only issue now, beside the codes and evap lines at filler neck is the motor feels week when going up a hill and kind of surges off and on a little. I added some injector cleaner today to see if does anything.

Codes and live data tomorrow. Thanks!