Ok, I am new to the website in that I have never posted. But I have been using the excellent advice on here as a guideline for issues with this car for about 6 years. Thanks to all.

2001 Montero LTD , just shy of 110k miles. Just did tune up with all the recommended parts on here. Irirdium plugs, NGK wires...etc. Changed the valve cover gaskets, the passenger side rear cam o ring seal, the spark plug oil seals, plenum gasket. Put it all back together and started fine, ran good. Took it for a test drive at about 8-10 miles set codes P0125 and P0173. After researching here, I tested the thermostat....good. Finally replaced the ECT. Ran like a champ for about 100 miles then set P0125 and P0170. Not sure what happened there why it changed from P0173 to P0170. Anyone have any idea what would cause this? I have checked all the vacuum lines on the plenum that I had off and all of the connections, everything looks fine, but there is obviously an issue there I am still getting a CEL but it changed. Cant imagine it doing that if it was an O2 sensor. Any help or direction would be awesome.

 

UPDATE: today sprayed starter fluid on all vacuum lines and fittings. No luck, idle is smooth. Reset codes and will see when she takes it out again if it sets the same codes.

 

did you read up on the codes.

p0125 indicates an issue that the car is not warming up after a set amount of time. check the sensor make sure its not faulty, if it works. check to make sure your thermostat is not opening/closing. may have to be replaced.

p0170 is a fuel trim issue. MISFIRE. you installed plugs and wires. DID YOU CHECK THE GAP on the plugs. that is first "simplest" thing to check, make sure wires are not faulty and not arching. but def check the gap on the plugs. were they pregapped? or you assumed so? you shoudl check. because this code DEFINITELY points to that it seems.

0173 is same as above. different bank. so it may be again something in the ignition system that is causing it to misfire. and you did do something in the iginition so double check. it says could be o2 sensor as well. but it hink the montero throwsout a specific code for that dont know if tis this.

 

Yes, I did research the codes. I ended up changing the ECT, that is when it changed from one bank to the other. Pulled thermostat out, boiled it and it opened and closed every time it was removed or put back in the water.

However, what I did do was assume the plugs were correctly gapped. Never even crossed my mind. Have to check that. Thanks. It runs fine and idles smoothe, just keep getting the codes. Does seem to idle a little high when the code is set and doesnt seem to set the code around town, just after a while now...say 60-100 miles at a time. Possibly the gap on the plugs. Man, never even considered that, thanks again.

 

Ok so, finally had time to work on it again Sunday. Changed the thermostat and put another ECT in. Didnt trust it as the codes changed after I put the last on in. So far, no codes...100 plus miles.

PS....pulled some of the plugs, everything gapped between .039 and .040, so we are good there. Hopefully everything is good now and it was a time thing with the thermostat. Thanks.

 

thats good news.. everytime i reset the ecu. codes usually come back on after 30 miles if i really didnt fix the problem

 

UPDATE: Everything was good for about a 100 miles. CEL came back on, set same codes. We took it on about a from WV to the NC Zoo. Light stayed on all the way down and while we were there. Started home and about Mt Airy, NC the light went off. Came back on shortly and stayed on until the other day, then it just went off and has been off for about 4 days now. Go figure...have no idea. Guess one day it will manifest itself again.

 

I have exactly the same problem and posted a new thread on P0170 error. My Mitsubishi Montero 1999 3.5L petrol V6 runs perfectly and about 100 miles after resetting the codes they come back again. P0170 and P0173 (both banks - Fuel mixture trim error). The fact that it occurs simultaneously on both banks makes me think it must be something that affects both banks and I think the main thing that could do that is in the air intake (MAF?).

I bought OBD software for my Mac (Auto Doctor) with a WiFi link which allows me to reset it. Did you ever solve your problem?

Thanks.

 

^Seems like a common diagnosis is a faulty MAF sensor. By any chance, are you using an oiled air filter?

 

No, I am using standard paper filters which have been replaced several times recently. What is the next step to evaluate the MAF system. Could it be a simple matter of replacing a sensor or is it a more major air intake system replacement? Thanks.