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Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8621
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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ONLY ***** . It seems that the Sensor issue is solved. Today

Customer Question

Doug ONLY *****Hi Doug. It seems that the Sensor issue is solved. Today I drove over 100 miles with no issues regarding the fuse. To be honest my car has quite a few issues. Today I fix an issue with a misfire code I was getting by replacing the ignition coils which arrived this morning by mail.The next problem I want to tackle is with my acceleration. When I floor the accelerator (in any gear) the car does not move. As I start to release the accelerator there is a point in which fuel starts flowing and the car accelerates. The funny thing is that if I slowly press the accelerator past this point the car continues to accelerate. Any ideas?
Submitted: 1 year ago.
Category: Mitsubishi
Expert:  Doug replied 1 year ago.

Hi again,

That's great news on the fuse.

When you floor the accelerator, does the engine rev up normally or even quickly but the vehicle doesn't move, or does the engine bog down and not rev normally?

Customer: replied 1 year ago.
It bugs down without revving up.
Expert:  Doug replied 1 year ago.


Is there any change if you unplug the air flow meter (the large square sensor on the air filter housing)?

I am stepping out on that break in just a few minutes I had mentioned earlier, but I will catch up with you as soon as I return.

Customer: replied 1 year ago.
That is way you're the expert. Disconnecting he Mass Air Flow Sensor had an effect. With it disconnected I can now floor the accelerator. What does this mean?
Expert:  Doug replied 1 year ago.

Cool.... it can mean a few things. The knee-jerk reaction is that the MAF is faulty, but there are other implications.

Specifically, when the MAF is disconnected the computer reverts to a "map" tune, it ignores all but critical sensor inputs... so no MAF no TPS no MDP no O2 readings etc. It just relies on the cam/crank sensor and a "Best guess" at your needs based on a predetermined fuel/timing map. If it runs more or less normally (problem resolved, though you may have "new" issues unplugged), then your mechanical and powertrain components (engine internal, injectors, exhaust etc) are all "ok".

So.... we need to figure out which is more likely the case... is the MAF bad, is there a problem with the input from the MAF, or is there some other sensor reading at fault.

Looking at the intake duct, is it full seated both on the throttle body end and MAF end? Is there any damage at all to the intake duct, like the baffle on the corner being broken off, the "hook" on the bottom that used to have the fuel line tied to it broken off, the PCV hose port broken off, etc?

Customer: replied 1 year ago.
I hope it is not the MAF as I just purchased it on 5/5/12 for $232. I just removed the duct and cleaned the MAF with MAF spray. Also cleaned the throttle body. Put it back together making sure everything seated correctly. The PCV hose is good and the PCV was replaced in 2014. I can't picture what you mean by the "baffle on the corner" or the "hook" on the bottom.I also disconnected to the battery for a few minutes to reset everything and drove for about 40 miles. Still the same problem. I tried flooring the accelerator in first gear and it just stalled and turned off. I also tried to floor it while in 4th and it stalled for a second and then it rev'ed up. My reflexes made me start to release the accelerator and the car started accelerating. So I don't know if the car accelerated automatically or because I started to release the accelerator.
Expert:  Doug replied 1 year ago.

If the MAF is new and only $232 it is certainly aftermarket and we do have huge problems with aftermarket electronics on these cars.... if you still have it, I would probably prioritize putting the old one back on and see if it changes the condition any.

With regard to the duct... on certain models (primarily early ones) on the back corner of the duct where it bends to go to the throttle body there is a triangular baffle attached that tends to break causing an unmetered air leak. Later models (I think around 03 or 04) they eliminated the baffle, so if you don't have it you may have a newer duct (or a hole there!). On the bottom center of the duct there is J hook molded in that originally had the fuel lines zip tied to it... this sometimes breaks off if people try to wrestle the duct off whiel the lines are still attached.

If you have the old MAF, lets swap it on there first though... there is a moderate possibility that the new part just failed.

Customer: replied 1 year ago.
Sorry. Don't have the original one. My duct still has the baffle. It is all intact. No holes on the duct.
Expert:  Doug replied 1 year ago.


Do we have access to a scan tool that reads live data so we can see what sort of numbers that MAF is putting out?

Customer: replied 1 year ago.
Boy do I wish I had that. Perhaps we check whatever else can be causing the problem.
Expert:  Doug replied 1 year ago.

Well basically your primary suspects here are going to be either unmetered air leaks (of which the common ones would be where you already checked) or individual sensor failures (MAF, TPS, MDP are the prime suspects). And for the latter... a scan tool is really needed to convincingly condemn anything.

Let me ask this... when you had replaced the MAF before, was it for this same condition or was it for something else? What was the result when the sensor was changed (if done for something else, was it fixed? were new problems created?, if for the same problem, was there no change?)

Customer: replied 1 year ago.
Firstly I don't know what are; TPS and MDP. Secondly, the MAF was replaced because we thought it was contributing to a hard idle problem. It turned out to be the Idle Air Valve. Replacing the MAF did not change anything nor caused any new problems.I just realized that today I only spayed the back side of the resistor on the MAF. Tomorrow or Thursday I will try spraying the front side.
Expert:  Doug replied 1 year ago.

Okay well that is good if it didn't change any conditions... that is a strong indicator it isn't your issue.
The TPS is the throttle position sensor, the sensor on the side of the throttle body with the wide electrical connector that looks impossible to unplug (and nearly is!). It measures throttle angle and delivers fuel based on the position. If it is reading incorrectly it can over fuel causing difficulty when pressing on the pedal, and when the MAF is unplugged it is ignored.

The MDP is the manifold differential pressure sensor, which is used as a cross check against the MAF reading. It is bolted to the top of the intake with a wire retainer holding the harness on (there are two like this up there, but we won't get into that right now).

We can definitely try cleaning that again tomorrow... have you had a Service Engine light set during this (apart from when we had the MAF unplugged)?

Customer: replied 1 year ago.
Morning. I'm back at it again. The cleaning did not work.Can you please send me a pinout for the MAF connector. Thanks.And please tell me what to test next.
Expert:  Doug replied 1 year ago.

No problem.
Looking at the connector on the MAF right side up (release button on top), the pins are left to right:

1) 5V reference

2) Barometer reading

3) MAF reading

4) Ignition 12V

5) Ground

6) Intake temperature reading

7) MAF reset

Note that none of the readings you get on there are going to be meaningful beyond checking your ground and reference voltage; we need a scan tool to read the calculations.

Customer: replied 1 year ago.
Hello Doug. This morning I decided "What the heck!" and took a trip to LKQ, the local Pick-your-parts junk yard. I found MAF replacement and tried it out. Now I can floor the accelerator with no problems stalling. I'll be honest, another symptom of MAF was that while idle and in gear (Drive or Reverse) the engine would slowly loose RPMs and finally stall and shut off. I did not mention it thinking that it was just another problem having to do with idle and the related sensors and valve. But replacing the MAF cleared this up.Now, perhaps tomorrow or Saturday I will begin to tackle the next issue. It is that the engine accelerates rough after first gear. The RPMs at which the vibration occurs depend on the speed of the vehicle. In Sports mode and aggressive shifting the vibrations occur between 3K and 4K RPMs. During normal driving and shifting the vibrations occur at lower RPMs.
I would have suspected the Motor Mounts but these are fairly new and I can rev up close to redline in first gear and feel no vibrations. So I'm thing fuel, air, electrical or any combination.
Expert:  Doug replied 1 year ago.

Hey that's great news!

Its definitely a hard lesson learned with the aftermarket sensors/electronics on these vehicles. It really does pay to stick with genuine parts. Hopefully it has been relatively recent since you bought the other MAF you can return it or at least exchange it and try again.

With regard to your vibration.... Is the timing belt over due? We sometimes see this occur when the balance shaft belt breaks. Apart from that.... that is something that probably is going to require a butt in the seat to experience to get a good idea of what is going on... if there is an air/fuel issue causing engine malfunction, if there is an exhaust flow issue preventing the engine from running smoothly, or perhaps way off that track if there is a transmission related issue occurring.

Customer: replied 1 year ago.
Unfortunately the MAF was purchased on 5/5/12. No luck on warranty there.The timing belt was replaced about two years ago. I purchased a timing belt kit and was planning doing this myself since the mechanic who replaced it suggested that the Crankshaft sensor may be bad again due to the misfire codes. But I got hit with the fuse issue which threw my plans out the window. I'm beginning to doubt the need to replace the timing belt now. Is there any easy way to isolate a possible transmission problem from a timing belt issue?
Expert:  Doug replied 1 year ago.

Oh okay so it was quite a while ago then! Given the track record on those, that isn't really that bad if you got 4 years out of it.
I wouldn't rush to judgment on the misfire situation until you have driven a bit with the working MAF... a bad MAF can very easily set misfires too as it is playing havoc with the fuel trims.

With regard to the vibration, the easiest thing is to just check the belt alignment.... easy being relative term here, as the belt has to come off to check the primary shaft timing anyway. But comparatively speaking, identifying it in the transmission is difficult. A set of line pressure tests to check for unusual fluctuations would be a good idea if we had strong reason to believe it is in the transmission. Given that it doesn't do it in 1st gear leans it toward transmission internal, however again this is one of those things where actual seat time in the car is the biggest helper. Some things you just have to feel/experience to get an idea of what is going on.
What I would do is check the belt alignment on the balance belt, and if you are about due for a belt job anyway, check the timing on the primary shaft (oil pump) to make sure it isn't out of phase. I would also check the condition of the transmission fluid that it is not burnt smelling, dark brown, or heavy with particulates/sediment. If it is any of those things, I would flush (not drain and fill) the system with fresh SPIII from either a Mitsubishi or Hyundai dealer (both are the only source of correct fluid) and compare behavior afterward.

Customer: replied 1 year ago.
What is the cost for this SP III? Can I get something similar at the auto parts store? How about Lucas fluids/treatments?
Expert:  Doug replied 1 year ago.

Sorry for the delay, I was out on a break. You don't want to put any additives into 40/50 series transmissions except as a last resort.

The SPIII from Mitsubishi is about $8 per quart list price. The Hyundai SPIII is often closer to $6-6.50 last I checked (I only work for Mitsubishi, so I'm not on top of Hyundais pricing).

There is no "good" replacement from the auto parts store. Just about all parts stores will direct you to either Dexron 3 or a universal ("multi car") fluid. Neither are acceptable long term fluids, especially if you are potentially chasing a fluid related issue.
There is one specific SPIII replacement made by NAPA. I have heard mixed reviews about it, and have to take into consideration that they are basing it on the SPII fluid (The same way the parts stores recommend Dexron and Dexron-base universal fluids).

The reason these are at issue is because of the fluid hierarchy. In a nutshell:

Originally Mitsubishi had SPI. It superseded to SPII.

SPII was compatible with Dexron 2.

Dexron 2 superseded to Dexron 3 (and became the base for universal fluids).

Dexron 2 and Dexron 3 are forward and backward compatible.

SPII superseded to SPIII.

SPIII is backward compatible with SPII, but SPII is not forward compatible with SPIII.

And so... Dexron 3 meets SPII requirements, but not SPIII.

Specifically, there is a different friction coefficient in the SPIII which causes the Dexron base fluids to slip a small amount more than designed. This results in increased friction wear and increased sediment as time passes. Not too much of an issue in the short term (unless you already have a slip issue then it can aggravate it), but in the long term it makes a normally unlimited mile transmission with regular maintenance a 50k-75k mile before frictions wear out and you need an overhaul type transmission.

Expert:  Doug replied 1 year ago.

Did you need further help with this or are we able to close this ticket out?