Good morning, afternoon, or evening depending on where you are! Headed to pick up my soon to be new to me 2001 Montero XLS and had some questions. It is currently throwing a few code P0431, P0155, and P0300) and I have looked them all up. The vehicle has sat for awhile so I tend to think its the catalytic converters (21 year old vehicle) but also have a plan to rebuild the ignitions components (all three coils, new plugs, new wires, new ECM), replace the EGR, the IAC valve, air and fuel filter, the EGR, and all three O2 sensors. I feel like those components will help give longer term reliability even if it doesn't fix the problem permanently BUT... before I go that route I would like to shove some seafoam down its throat and in the tank to clean everything out in the exhaust system.
I will have to drive it about 300 miles back home the day I purchase it but the gentlemen I talked to said that once its warmed up it runs fine. Because I am getting a good price (during this crazy used car price time we live in) I don't mind putting in the work to go through the plugs and wires and the rest of it all, including the front Y pipe with cats, if I have to (about $500 for all the listed parts and another $860 for the Y pipe if needed) but as it is a 3rd vehicle meant to be the bomb around it also needs to be dependable.
Tracking I need a manifold gasket in order to do the plugs and wires, anything else? (yes I will be searching the forums)
Looking at the forums it appears I will need three coils total (one with the white connector for cylinders 4 and 6 and two with the black connector for 1,2,3,5, accurate?
So... fire away with thoughts and suggestions,

UPDATE- just saw a great post that talked about not blindly throwing parts to address issues because its not like other vehicles that are built with not great parts. I still feel like the plugs, wires, coils make sense with the mileage of the vehicle as does an air filter and a new belt. The IAC valve, PCV and EGR also seem to make sense just due to age but still searching....

 

Don't worry about the manifold gasket and coils for now. I've re-used gaskets multiple times. Replace it if it's damaged.
I'd say, the #1 item to adress is figuring out where the misfire is coming from. Random misfire can be a pain to diagnose. Keep in mind - it is not necessarily a "misfire" but rather an uneven cylinder power contribution. I'he seen the spark plug tubes being flooded with oil leaking from valve cover gasket and causing the misfire. Definitely worth checking that among the first things.
Leaky valve seals could under some conditions can contribute to the random misfire condition.
Another important item to adress is the O2 sensor malfunction. Not working properly that can cause all sorts of issues, including the misfire.

 

So there is a higher pitch whine coming from the engine bay, not deafening but noticeable. Thinking serpentine belt and idler pulleys ( they are a bit dry and loose) and likely the idler pulley as well. The idle is VERY low and tends to stumble and rumble when in gear or park at a stop. Doesn’t shut off just really low. Running some fuel system cleaning through is and some oil stabilizer.
Thoughts?

 

Made the trip home 250ish miles, REALLY low on power. Brakes good, suspension not bad at all, transmission kept up fine but it need the power back to match the revs. What I mean is that the revs are really low at highway speed (like 1800rpm) because (I am assuming) that the misfires are not providing full power or matching RPMs so when the transmission shifts into 4th and I am going anything other than 75 it shudders because the revs are low.
Also had a thought on the drive (Instill need to read on it ), if the EGR valve is not functioning properly will is trip the O2 sensor since the EGR send hot air back through the manifold to help with CAT light off?!?!? Just thinking out loud. Lots of other small things but for $4000 I think this will turn out to be a good buy

 

While both EGR and O2 sensors are part of the emissions control system, their role and function excludes one malfunction from triggering a code for another one.
You do not have a code for EGR valve or solenoid malfunction and you do not have a symptom of stuck open EGR valve. Do not do anything to EGR at this time, besides checking for carbon build up/blockage in the EGR manifold. You will be able to see the ERG passage in the intake manifold when you remove it to get to the spark plugs.
The O2 sensor code malfunction you have is important one to address. It is for B2S1 (Bank 2, Sensor 1). This is a pre-cat sensor on the driver side. It is responsible for reading O2 levels in the exhaust (indication of how complete combustion process is). Without proper feedback from that sensor, computer will not provide proper fuel levels to the cylinders. I can't guarantee it, but it is possible that the lack of power you describe is related to that malfunction. If you are able to pull live data from the OBDII port, you can see is the system is working in Closed Loop mode (proper function), or in Open Loop mode (back up/limp mode). Check wiring for the B2S1 O2 sensor, make sure there is no breaks / melted wires there. If all checks out but it still doesn't work - replace the sensor. Get the one with the plug, instead of a pigtail that you have to wire yourself. it is just a little more expensive, but worth knowing that it wired in correctly.

 

So one thing I forgot to mention was that the vehicle sat for about three years, hoses seem ok but seals worry me a bit as does bad fuel causing the misfiring, plug fouling, and other age stuff. Lots of parts coming in to fix stuff, I’ll be looking at the timing belt in the near future. I’ll be scanning the threads here for advice. Wish me luck

 

So checked the wiring for the upstream left side (B2S1) and it seemed fine, checked the plugs wires for routing, reset the faults with a battery disconnect. The idle was extremely rough and stumbling and within about 5 or 6 seconds the service engine light came on. The good news is that I think the squealing problem will be fixed with a new belt, tensioner and idler pulleys. After sitting so long the bearings in all of them were rusted and I could almost see my reflection in the belt.

 

What code did you get immediately upon restart?

 

I don’t have an OBD 2 reader, I need to borrow one today and see what it’s spitting out.

 

Sorry to ask this but it will be a bit before my manual gets in and I don’t want to wait till it was here to start so... I need some bolt torques
both idler sprockets
serpentine belt tensioner bolts
all the bolts involved in replacing the plugs and wires (intake manifold and EGR valve bolts)

I don’t think the coils or O2 sensors are torque critical, German torque without being stupid.
Thanks in advance for any help, just trying to get her all fixed up and in shape