Offroadmuch
Explorer
Last edited:
How is the idle controlled on a 2003+ (3.8L) Gen3 Monty?
- Thread starter haolepinoy
- Start date
Offroadmuch
Explorer
.
KyleT what code do you think it is? Lean left bank?
I might have to find someone who can make headers. Should be a quite a few in SoCal.
Offroadmuch
Explorer
Came here today. They assured me they would figure it out no problem for $100.00....
We shall see....
Offroadmuch
Explorer
They checked it out and said it is throwing a P0102 code. I took my new MAF unit that I had ordered previously and told them I was going to install it until my air box was starting to crumble. They said they were going to install the new MAF and "clean" the throttle body assembly and check out the performance. Said they would probably be done today and then keep it overnight to give it a cold start in the morning to make sure all is well. I will post results (and cost of the work) when I get them.
haolepinoy
Incomplete Idiot
Be careful to read the label on whatever MAF Cleaner you are using...
For some reason not specified on the label our Karmen Vortex style MAFs do not respond well to chemical cleaners. I have no idea why, but it's written there in #10 in case you missed it.
For some reason not specified on the label our Karmen Vortex style MAFs do not respond well to chemical cleaners. I have no idea why, but it's written there in #10 in case you missed it.
haolepinoy
Incomplete Idiot
Testing the Volume Air Flow Sensor
I guess since I started this mess of a thread I'd better chime in with something semi-profitable after dealing with these issues for the last two years. Here goes...
Regarding the Volume Airflow Sensor (Mitsu's name for the MAF):
First, it may or may not be the cause of your issue, and unless you put it to the test you're gonna throw a lot of money at the idle gremlins. The sensor is actually a combination of three different sensor readings that combine to tell the PCM how much combustible air is entering the throttle body. There are tests for all three readings.
Testing the Volume Air Flow Sensor itself (see FSM 13Ac-2 thru 17):
You'll need some kind of scanner that reads live data to test this one. It is Item #12 on the universal scanner list. With the engine running and warmed up to normal operating temperature you should get between 17 and 43 Hz at idle, between 64 and 104 Hz at 2,500 rpm, and the Hz should increase smoothly with engine speed.
Testing the Barometric Pressure Sensor (see FSM 13Ac-17 thru 43):
This test will also involve using the scan tool. It is Item #25 on the list. With the ignition on, record the kPa or psi or whatever pressure reading your scanner uses. Standard values should be 101 kPa at 0m, 95 kPa at 600m, 88 kPa at 1,200m (you'll likely need to do the unit conversions). I found my Baro sensor to be quite off. At 184', the exact altitude in my driveway, I was getting 14.2 psi (or 97.9 kPa at 56m)...basically it was telling my PCM that my Monty is sitting at around 600m when it was actually only at 56m...so it was expecting thinner air than it was actually getting.
Testing the Intake Air Temperature Sensor (see FSM 13Aa-17, 13Ac-44 thru 60):
This test has two parts. The first is to again read the live data on the scan tool. It is Item #13 and should match the actual temperature at the sensor (read with a thermometer of some sort). The second part involves reading the resistance between terminals #5 and #6 while raising the temperature with a heat gun of some sort. Standard values should be 2.3-3.0 kiloohms at 68*F, 1.0-1.5 kiloohms at 104*F, 0.56-0.76 kiloohms at 140*F. When I tested my IAT the values were on the edge of the ranges.
Conclusion: well, if you test these and find any or all sensors to be grossly misreporting data to your PCM then you may have a problem. In my case my BARO reading was off, but I doubt that it was a major factor or the only factor in my idle issues (for reasons I'll explain later). But in order to truly understand what kind of problem you have you need to understand how to listen to your 21st century vehicle because this honestly may not be your only or most significant problem. YOU MUST HAVE A SCAN TOOL OF SOME SORT IF YOU PLAN TO DIY YOUR GEN3 MONTERO...period. You do not need the MUT-II or III thingy from Mitsu HQ though. Almost any scan tool that reads live data will help you with 90% of your diy diagnosis work...especially fuel trims.
I broke down and got a decently priced scan tool after realizing there was no way around this...and it was cheaper than throwing a few sensors at the issue with my fingers crossed. I ruled out the EGR, the Throttle Body Actuator, the O2 Sensors, the Coolant Temp Sensor, and a few other expensive variables by diagnosing their health with a scanner (and the FSM). By reading and interpreting fuel trims I learned that I had worse problems that a dirty VAF or loopy Barometric Pressure Sensor. My Long Term Trims were pegged at +25% (no up or down), meaning my engine was running super lean (way too much air reporting to the O2 Sensors). My problem was that air was entering the combustion cycle somewhere after the throttle plate, primarily through a cracked exhaust manifold and dry-rotted vacuum hoses and honestly who knows what else (probably some gaskets too). And sadly, those aren't my only problems so I can't even isolate and whack the moles one by one (also have a bad alternator covered in oil, leaky cam seal, weak battery, a shortage of time & money, poorly installed timing belt by PO's mechanics, mismatched spark plugs by the same hacks, and on and on...smh, what a year it's been.)
My Monty is still sitting in a few dozen pieces (it was a few hundred a week or two ago...yay for progress), so I still haven't figured everything out or fixed all my gremlins. I just know that in my experience there are always more than one gremlin at work at the same time.
I guess since I started this mess of a thread I'd better chime in with something semi-profitable after dealing with these issues for the last two years. Here goes...
Regarding the Volume Airflow Sensor (Mitsu's name for the MAF):
First, it may or may not be the cause of your issue, and unless you put it to the test you're gonna throw a lot of money at the idle gremlins. The sensor is actually a combination of three different sensor readings that combine to tell the PCM how much combustible air is entering the throttle body. There are tests for all three readings.
Testing the Volume Air Flow Sensor itself (see FSM 13Ac-2 thru 17):
You'll need some kind of scanner that reads live data to test this one. It is Item #12 on the universal scanner list. With the engine running and warmed up to normal operating temperature you should get between 17 and 43 Hz at idle, between 64 and 104 Hz at 2,500 rpm, and the Hz should increase smoothly with engine speed.
Testing the Barometric Pressure Sensor (see FSM 13Ac-17 thru 43):
This test will also involve using the scan tool. It is Item #25 on the list. With the ignition on, record the kPa or psi or whatever pressure reading your scanner uses. Standard values should be 101 kPa at 0m, 95 kPa at 600m, 88 kPa at 1,200m (you'll likely need to do the unit conversions). I found my Baro sensor to be quite off. At 184', the exact altitude in my driveway, I was getting 14.2 psi (or 97.9 kPa at 56m)...basically it was telling my PCM that my Monty is sitting at around 600m when it was actually only at 56m...so it was expecting thinner air than it was actually getting.
Testing the Intake Air Temperature Sensor (see FSM 13Aa-17, 13Ac-44 thru 60):
This test has two parts. The first is to again read the live data on the scan tool. It is Item #13 and should match the actual temperature at the sensor (read with a thermometer of some sort). The second part involves reading the resistance between terminals #5 and #6 while raising the temperature with a heat gun of some sort. Standard values should be 2.3-3.0 kiloohms at 68*F, 1.0-1.5 kiloohms at 104*F, 0.56-0.76 kiloohms at 140*F. When I tested my IAT the values were on the edge of the ranges.
Conclusion: well, if you test these and find any or all sensors to be grossly misreporting data to your PCM then you may have a problem. In my case my BARO reading was off, but I doubt that it was a major factor or the only factor in my idle issues (for reasons I'll explain later). But in order to truly understand what kind of problem you have you need to understand how to listen to your 21st century vehicle because this honestly may not be your only or most significant problem. YOU MUST HAVE A SCAN TOOL OF SOME SORT IF YOU PLAN TO DIY YOUR GEN3 MONTERO...period. You do not need the MUT-II or III thingy from Mitsu HQ though. Almost any scan tool that reads live data will help you with 90% of your diy diagnosis work...especially fuel trims.
I broke down and got a decently priced scan tool after realizing there was no way around this...and it was cheaper than throwing a few sensors at the issue with my fingers crossed. I ruled out the EGR, the Throttle Body Actuator, the O2 Sensors, the Coolant Temp Sensor, and a few other expensive variables by diagnosing their health with a scanner (and the FSM). By reading and interpreting fuel trims I learned that I had worse problems that a dirty VAF or loopy Barometric Pressure Sensor. My Long Term Trims were pegged at +25% (no up or down), meaning my engine was running super lean (way too much air reporting to the O2 Sensors). My problem was that air was entering the combustion cycle somewhere after the throttle plate, primarily through a cracked exhaust manifold and dry-rotted vacuum hoses and honestly who knows what else (probably some gaskets too). And sadly, those aren't my only problems so I can't even isolate and whack the moles one by one (also have a bad alternator covered in oil, leaky cam seal, weak battery, a shortage of time & money, poorly installed timing belt by PO's mechanics, mismatched spark plugs by the same hacks, and on and on...smh, what a year it's been.)
My Monty is still sitting in a few dozen pieces (it was a few hundred a week or two ago...yay for progress), so I still haven't figured everything out or fixed all my gremlins. I just know that in my experience there are always more than one gremlin at work at the same time.
haolepinoy
Incomplete Idiot
Regarding this "test", the reason this worked wasn't necessarily because the VAF was malfunctioning. When the PCM detects a malfunction in the sensor (aka disconnecting it) it reverts to a fail-safe mode: "uses the throttle position sensor signal and engine speed signal (crankshaft position sensor signal) for basic injector drive time and basic ignition timing from the pre-set mapping. Fixes the IAC motor in the appointed position so idle air control is not performed." (FSM 13Ab-20) That is why Fernandez reported a steady 4.5 on the Throttle Position Sensor and 875 rpm idle. The sensor may have been bad, but testing it in this way would never have determined it. It just fooled the PCM into going "dumb" by ignoring its sensor inputs (many more than just the VAF inputs).
haolepinoy
Incomplete Idiot
The MAF issue and the Lean Left Bank issue are most likely two separate issues. If your VAF sensor was faulty previous to when you tried to remove it and clean it, it would have affected both engine banks equally. The fact that only your Left Bank was running lean means you had an issue only affecting that side of the engine...almost certainly the cracked manifold you mentioned. The crack in the manifold causes combustible air to be introduced to the exhaust gas right before being read by the O2 sensor. The sensor reads the exhaust as lean due to the presence of all that unburned O2, telling the PCM to dump more fuel into that bank and causing overfueling issues and a bad Air-Fuel mix. Your engine may be running a perfect 14.7:1 Stoichiometric ratio, with everything upstream working fine...but that crack makes the one O2 sensor think things are not well upstream, and by the PCM trying to compensate for the false data you get the idle issues.
Now that you've gone after the VAF with cleaner and tried to replace it you may have caused another issue (the P0102 code), but fixing it will not solve the Lean Left Bank code from before. You need to repair or replace that cracked manifold too.
I've had a hairline crack like in the photo on my 98 3.5 with zero performance issues, either driving or on the scope. Put some high-temp patch on it as a temp repair for diagnosis, see if it makes a difference before you replace it. Google images of "cracked exhaust manifold" and you will see what bad ones look like. I'd tend to think that it would take something more than a hairline crack to significantly throw off exhaust gas levels, but again, I've only dealt with this once on my Montero so I don't know what the range is for having problems.
Last edited:
Offroadmuch
Explorer
They finished it all up. It runs better. Idle is smoother although it does not feel perfect, like it should be a few rpm's faster to give it a more smooth balanced feeling. Cost was $305. I think I got a little overcharged for what was done. I hate to be suspicious of mechanics but I am. If I believed that the mechanic knew enough about my car, engine and troubleshooting, as described by Haolepinoy I would not mind the cost at all. I am not saying they did anything wrong but I am not completely convinced it was exactly the correct repair either.
Swank Force One
Adventurer
Nope.
Wish i could trade junkyards with you, though.
Wish i could trade junkyards with you, though.