How is the idle controlled on a 2003+ (3.8L) Gen3 Monty?

[Offroadmuch]

View attachment 419491
Pictured here is the (inside view) top of the airbox with the MAF still attached due to the mounting bolts spinning as the plastic cracks. Therefore I might try to just clean. To all reading PLEASE BE ADVISED THAT THERE IS MAF CLEANING FLUID. I say this because some may use brake or carb cleaner. MAF cleaner is supposed to "more gentle" for lack of better terminology. I may try this and scrap the replacement if it is going to destroy my air box assembly. I will update with what happens.

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I should add that after this failed attempt to unbolt my MAF from the airbox cover and also unplug the wiring I reinstalled everything since I couldn't get the MAF off and I needed to drive my truck to work, I now have a sputtering, hesitation when starting from a stop. So that is even more frustrating. I don't think that plastic broke enough to have an air leak so I am not sure how I could have a new performance problem by using the old parts that were working perfectly.
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I started all of this due to uneven-low idle and a recent service engine soon light was on. Local shop scanned it and I had lean condition in bank 2. They cleared the code and offered a bunch of possible solutions so I decided to try a few on my own instead of paying them to guess.
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So it looks like I am an official member of the Gen 3 Electrical Gremlins club.
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Maybe my next overland truck will be a 1970 Chevy V-8 350 of some kind....

 

[KyleT]

Lean bank codes are also a result of cracked exhaust manifolds. Not sure if that was posted before but check yours for a crack.


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[Offroadmuch]

Lean bank codes are also a result of cracked exhaust manifolds. Not sure if that was posted before but check yours for a crack.


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Fantastic! I will check that out.
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Anyone know a good exhaust place in Orange County that can check and weld?

 

[KyleT]

The manifolds are cast and I’ve not seen anyone post up a success story on welding them


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[Salonika]

Are you lean at idle or under load? A small air leak downstream from your volume sensor can give you lean & rough idle. If it's only a small air leak, it might not show up lean under load. Also start by re-checking things related to what you previously just had messed with, if the behavior changed as a result of your messing around, your problem might be in that neighborhood. Also look up the propane trick for locating air leaks.

 

[Offroadmuch]

Are you lean at idle or under load? A small air leak downstream from your volume sensor can give you lean & rough idle. If it's only a small air leak, it might not show up lean under load. Also start by re-checking things related to what you previously just had messed with, if the behavior changed as a result of your messing around, your problem might be in that neighborhood. Also look up the propane trick for locating air leaks.

I think it is lean at idle only. Has always had a fairly rough idle. Maybe better when the motor is hot but still a little rough. The hesitation and sputtering is new. It almost feels like it is missing. As the RPM's climb it will get to say 1400 then sputter and the whole truck shakes for a second and the. The motor resumes and works fine. Only happens during acceleration on the lower end and only since I fooled around with trying to remove the MAF. I will re-examine everything around the air box I take it off and spray cleaner all over it. etc...
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And FYI, the MAF I ordered from ebay is marked with a Mitsubishi sticker but the internal small electric parts are formed slightly different so I am not sure it is genuine. I paid about $80 and it is new not refurb'ed sooo watch what you get for these aging vehicles.

 

[Offroadmuch]

Drove this morning before I got any work done. By the time I came home my SERVICE ENGINE SOON light was on, hesitating all over the place. Baught a can of MAF cleaner. Took off the airbox cover and noticed it was not on quite right so that was my fault for working on the car in the dark last time. Disconnected both battery terminals and touched them together to drain energy and clear the SES light. Sprayed the heck out of my existing MAF and resinstalled. Test drive: SES light was now off, idle was about 500 RPM while in drive and stopped. A smooth 850 while in park or neutral. With AC on it was pretty smooth and about 700 while stopped in drive. It does seem smoother overall. Less shaky during idle under all conditions. Probably the best idle compared to my last 15,000 of ownership. Hesitation and sputtering gone. Probably due to my crooked install last time. Overall the engine ran great. These motors are fantastic when running right. I am going to consider this cased closed for now.

 

[Rod]

Nice to hear....I will need to pay attention when I clean out my MAF

 

[Salonika]

It is amazing to see how sensitive a gas engine is to proper air metering. Pop off a vacuum hose on your plenum once at idle and see how bad it makes the engine run. Hold your finger over the hole so you can control it. You'd never think such a small amount of air can cause such a big effect.

 

[Offroadmuch]

It is amazing to see how sensitive a gas engine is to proper air metering. Pop off a vacuum hose on your plenum once at idle and see how bad it makes the engine run. Hold your finger over the hole so you can control it. You'd never think such a small amount of air can cause such a big effect.

It also makes me really hate all of the sensors in modern vehicles. My 1972 Chevy Chevelle didn't have a single sensor and ran great. No ABS, no O2, no OBD2, if it ran crappy you knew something needed fixed. Simple. I am seriously going to look for a truck, SUV, Jeep, something from the 70's for when I retire and can spend more time Overlanding. Just start with a fresh rebuild or new crate motor.

 

[Salonika]

I only started learning computerized engine controls in the last 10 years. I think they are great but my biggest gripe is that the diagnostic equipment needed to do repairs is too expensive.....diagnosing sensors before replacing them is usually impossible (wave form diagnostics for cam & crank sensors for example). If I had all the goodies that a good garage has, I'd be all set.

 

[coffeegoat]

Certainly on the emissions side things get more complicated without much gain in performance (though depending on where you live emissions may be valuable "performance.") However, just look at some of the numbers for engine weight, displacement, MPG, power, torque, etc, and you can see the effect all of those fancy whiz bang sensors have.

I get frustrated as much as the next guy with bad sensors, and I can see the draw of a much simpler engine that you can fix with a hammer, duct tape, and some JB weld - I think it really comes down to the age of the vehicle and what you expect from it. I don't miss starting my engine up 5 minutes early to get warm, playing with choke settings, re-jetting carbs to compensate for altitude, and all the other gremlins.

I agree with Salonika that what I would really like is a better way to diagnose issues, check engine lights are an after-the-fact indicator that things "aren't quite right," but often the error codes don't give you the info you need to solve the issue. I'm curious if someone could rig up some sort of app to read all the data from a OBDII scanner, record it over time, and then use crowd sourcing to track down issues. So if the data showed your engine runs 5°F colder than average you'd start thinking about checking the coolant temp sensors, if the fuel trims were 5% higher than average you'd look for a vacuum leak, etc. That way you could find the problem before it actually popped a check engine light and hopefully have a clue where the issue actually is.

 

[Offroadmuch]

Well folks, my Service Engine Soon light came back on. Engine was warmed up, driving with 4 passengers, A/C on. Came to a red light and the idle went down to about 425ish and the SES light lit up. Bummer. Apparently cleaning off my MAF did not help. I will be moving on to try to figure out what is wrong. Maybe a downstream 02 sensor? I might try to take my truck up to Van Nuys to C&A so the Mitsubishi Master Techs can give me an opinion.
14122 Vanowen St, Van Nuys, CA 91405
Never been there but heard they are good.

 

[Swank Force One]

Downstream o2 shouldn't affect how the truck runs.

Bummer man.

 

[KyleT]

What code?


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