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Doug
Doug, ASE Certified Technician
Category: Mitsubishi
Satisfied Customers: 8547
Experience:  Mitsubishi employed and Factory trained ASE certified technician
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Mitsubishi Mirage LS: My car one day started to have a little

Customer Question

My car one day started to have a little rough idle and wanted to stall sometimes. I took it for a check at autozone and got code P0-401. Yesterday I arrived home after a 30 minute run and when I parked my car and leave it idling it suddently stall which was rare and I turn it on again and seconds after it stalled again. Turn it on for a 3rd time and didn't stall or had rough idle. Checked it again at autozone and got same code. I tried cleaning the valve with carb cleaner, saw a video on youtube on how to test an egr valve with a vacuum pump. Bought a vacuum pump and tested it un mounted the valve diaphragm moves to the open position when vacuum applied and holds vacuum for atleast 5 minutes which I tested it. Also tried testing it with the car on at operating temperature and it won't stall or try to stall as video says it should when valve is open in idle. So my mechanic removed the Intake manifold and proceeded to clean the passages both with carb cleaner. Tried doing the same thing after cleaning the passages with car on and it still won't stall or try to stall. I don't know what the problem could be. I already tried a lot of stuff and still same code. My sister has the same car and I applied vacuum to her cars egr valve while idling and it did tried to stall, so I proceeded testing her egr valve in my car to confirm mine was good and installed it and turned on the car and let it get to operating temperature and then proceeded to apply vacuum to the egr valve and car did nothing, didn't tried to stall. So I started to think the problem could be no gas circulation is coming through the intake manifold passages. Any help?
Submitted: 10 months ago.
Category: Mitsubishi
Expert:  Doug replied 10 months ago.
Hi, When you compare the vehicles, both vehicles vacuum hoses are connected identically right? And when you apply the vacuum manually you are doing so directly to the valve?If the systems are hooked up identically and the valve is transferred and manually opened, it should behave the same unless either the intake passages are clogged or the head passages are clogged.That said... it really shouldn't cause your vehicle to idle poorly in itself. At idle if the hoses are routed correctly the valve should be closed anyway, so there is something else going on there. What is the state of the engine? Compression tested recently, tune up components, idle valve operation checked etc?
Customer: replied 10 months ago.
Hoses are similar, identical valve. The problem I think about is the when you open the valve with a vacuum pump my car won't try to stall or anything on the other end my sister's with just 5in hg will try to die fast. So for me and for what I have read that means there's no flow trying to or passing through the valve. And since both intake manifold passages are already been cleaned. The problem is elsewhere. What is the head passages and where is it located?
Customer: replied 10 months ago.
Also when I removed the idle air valve what should it do? Should it move or something?
Expert:  Doug replied 10 months ago.
Right... it should stall. If it does not and the valve is known good, then you would only suspect a clog in the intake manifold or the cylinder head in the EGR ports. However this is assuming the rest of the vehicle is in normal running condition. This is why I am concerned about the rest of the state of the vehicle, as a clog in the EGR would not cause the vehicle to run rough or want to stall. Just the opposite, if the valve is shut it will have no effect, regardless of the condition where it doesn't flow enough when opened.The passage in the head is behind the intake manifold. When the manifold is off there is a passage below the #4 air port, that is where the passageway is in the head.You do not need to remove the IAC to test it. Just run the engine and idle it as best you can (use the gas pedal if needed) and then turn the AC on and see if the idle goes up or if it goes down.
Customer: replied 10 months ago.
When I turn the AC on it goes idle goes down. When we removed the intake manifold I looked at the hole from where the gas should go to the intake manifold and it looked atleast there clear. I even shirt tried cleaned atleast there.
Customer: replied 10 months ago.
This is my intake manifold. Where is the head passages?
Expert:  Doug replied 10 months ago.
Thanks.The passages aren't visible in that picture, or even with the manifold mounted. I'll see if I can find a photo for you.With regard to the IAC reaction... that is a bad result and very likely related to your primary drivability issue.With the engine idling again, turn the steering wheel hard one way and load up the power steering pump. Does the idle go up or does it go down?
Expert:  Doug replied 10 months ago.
Here are the passageways, the one on the intake you mentioned was already cleaned (hopefully effectively) and the one in the cylinder head is in the other picture.
Customer: replied 10 months ago.
This is with the AC off
Customer: replied 10 months ago.
AC on
Expert:  Doug replied 10 months ago.
Yeah it looks like your IAC is stuck open/not closing. This would cause the poor idle condition at time, the stalling at times, and the insufficient EGR flow as the excess air coming in will cause the pressure to be incorrect.Lets swap the IAC from the test vehicle and see how it runs.
Customer: replied 10 months ago.
Yea the intake manifold one I think it was succesfully I spent a full carb cleaner spray bottle and even used a little screwdriver to remove carbon that was really glued to the passages. And I can tell I removed a lot.Your second picture yes that's the hole ai mentioned before that I passed a shirt just right there. For it to be cleaned efficiently I have to remove the intake manifold again and it also has to be removed or it can be cleaned mounted?
Expert:  Doug replied 10 months ago.
I wouldn't even worry about that hole in the head right now, you'd know if it was an issue as it would be packed solid.Lets get that IAC swapped since we know that is causing an issue since it is not idling-up properly anyway.
Customer: replied 10 months ago.
Should I remove it from it's 3 screws or I should remove it entirely?
Customer: replied 10 months ago.
I also have this installed but I don't know if ut will affect. Because car still lowered rpm's when AC was turned on.
Expert:  Doug replied 10 months ago.
Just the three screws but be careful on removal there is a o ring behind there.... sometimes it stays stuck to the valve, other times it wants to fail. So keep a hand under it until you verify it stayed attached so you don't drop it.The intake is a minor concern, but knowing that the idle goes down when the AC is turned on (by design it should go up 100-200 rpm, then drop 100 rpm or so resting either at the same RPM as off or just a bit above), we need to address that first.
Customer: replied 10 months ago.
I noticed when I turn the AC on rpm's go up but rapidly go down to lower than when AC off. I can try with my sister's car IAC valve and see if it fixes the problem right?
Expert:  Doug replied 10 months ago.
Okay that would potentially change things. If the AC is making the idle go up first, then that would be normal operation. However it should still rest at the same idle speed or just above same idle speed with AC on, so you are still dealing with an issue there it sounds like. If it is bogging down with the AC on either the IAC is not opening properly (but trying) or there is excessive load from the compressor putting more strain than normal on the idle.I would still try the other IAC, there is still a chance there is relation there.
Customer: replied 10 months ago.
In this short video You can see car at idle and AC off and see near the end of the video how from time to time rpm's bounce up and down.
https://vid.me/6DgY
Expert:  Doug replied 10 months ago.
Is that when the AC is turned on with the donor IAC?
Expert:  Doug replied 10 months ago.
Or does it just randomly do that even with the AC off?
Customer: replied 10 months ago.
That's my cars IAC and it just radomly do that with AC off.
Expert:  Doug replied 10 months ago.
Gotcha. Lets try the donor IAC as we planned and see if there is change in behavior.If not, we will want to talk like I mentioned before about compression, tune up, etc.
Customer: replied 10 months ago.
https://vid.me/DNti
In this one you can see when I turn on the AC what the rpm's do.
Expert:  Doug replied 10 months ago.
Okay that is more like it... if that is the original IAC, that is normal operation, that is very different from what we were talking about before.In that case... before getting into pulling the manifold or head for EGR port cleaning, have you checked your compression and tune up components? Again while the EGR not stalling the car is a concern, it shouldn't affect idling unless there is something more going on.
Customer: replied 10 months ago.
So my IAC appears to be ok? But they shouldn't be bouncing up and down randomly.
Expert:  Doug replied 10 months ago.
If it is going up when you turn the AC on then settling when the AC actually engages, then yes. It is hard to tell what is happening since I can't see the AC being operated only the gauge, but I'm imagining that is what is going on.... idle, then ac is pushed, the idle goes up, the ac engages, then idle settles down. If that is not what is occurring, the IAC is suspect. If it is what is occurring, it is likely OK.
Customer: replied 10 months ago.
So tell me with more details what you mean with tune-up components? I changed spark plugs some months ago to NGK. I also changed the spark plugs cord set
Expert:  Doug replied 10 months ago.
NGK plugs that is good, new cords that is good too.Can you compression test the engine so we can see the health of the engine?
Customer: replied 10 months ago.
How's that done?
Expert:  Doug replied 10 months ago.
You'll need to borrow a compression tester since you do not have one; most auto parts stores loan these out. You'll remove all four spark plugs and unplug the injectors (so there is no fuel spraying while you crank the engine), then install the compression tester into a cylinder and crank it 4-6 revolutions. Take a reading and then move to the next cylinder.I am stepping out on my afternoon break so that will give you time to get that looked into.
Customer: replied 10 months ago.
What 4-6 revolutions means? And also I will have to do that another day since I cannot go right now to verify if I can rent one
Expert:  Doug replied 10 months ago.
Sorry for the delay, 4-6 revolutions of the engine. You can just count the loping sound of the engine is fine.We can regroup at any time, just let me know; you may still want to try that other IAC, however I think there will be something more in play based on your gauge video, it looked like it was working properly there.
Customer: replied 10 months ago.
Just took this video now. Behaved different. https://vid.me/Ao8Z
Customer: replied 10 months ago.
When I turn the wheel hard and fast while idle with AC off rpm's go down.
Customer: replied 10 months ago.
That video was with the car at a lower temperature
Expert:  Doug replied 10 months ago.
Sorry about that, I'm back now.Yeah, definitely lets try the other IAC.
Customer: replied 10 months ago.
Ok I'll swap it tomorrow morning and will keep you updated.
Expert:  Doug replied 10 months ago.
Sounds good.
Customer: replied 10 months ago.
See on this video when the AC engages the rpm's go up and down and then like they lower even more and back up.
https://vid.me/I4K6
Expert:  Doug replied 10 months ago.
That could be any number of things out of context. The IAC can do that, but also if the evaporative system runs its test it will do that too, among other causes both normal and abnormal.
Customer: replied 10 months ago.
So I should try with aother IAC first and if problem persists then I should check compression?
Expert:  Doug replied 10 months ago.
Yes, since you do still have somewhat-IAC related behavior and you have a good donor available, I would try swapping the IAC first. Then a compression test would be in order to check internal health in relation to the idle/stall issue.
Customer: replied 10 months ago.
Ok. What are the ideal values for compression?
Expert:  Doug replied 10 months ago.
This is a 1.8 right?
Customer: replied 10 months ago.
Yes
Expert:  Doug replied 10 months ago.
Spec is 199 psi per cylinder, maximum variance 14 psi.
Expert:  Doug replied 10 months ago.
It can run as low as 151 psi as long as the cylinders are balanced, but the lower it gets the worse the output is. Under 150 psi it goes into non-running/unreliable running condition.
Customer: replied 10 months ago.
So with a compression tester I installed where the spark plug goes with injectors disconnected and then I try to start the car and that would give me a compression reading?
Expert:  Doug replied 10 months ago.
RIght, you'll hear the engine lope as compression builds on each revolution. After 4-6 revolutions read the gauge then move it to the next cylinder, release the pressure on the gauge and do it again.
Customer: replied 10 months ago.
I don't quite understand the meaning of 4-6 revolutions. Can you explain that for my understanding please?
Expert:  Doug replied 10 months ago.
As you crank the engine you will hear the engine lope on each compression cycle. Like it strains as you are cranking. You'll hear that 4-6 times then stop.
Customer: replied 10 months ago.
I let it do that for 4 to 6 times then I should stop and see the readings of the tester?
Customer: replied 10 months ago.
Also I should have all 4 injectors disconnected right? What about spark plugs? One by one or remove all 4 before testing?
Expert:  Doug replied 10 months ago.
Plugs don't matter, you can take them all out if you want or one at a time. Unplug all the injectors though so they do not spray... if they are spraying fuel when you compression test it will cause the readings to be off.
Customer: replied 10 months ago.
Ok I'll try the IAC when my sisters car is available and eventually I'll have to buy a compression tester at autozone. Since here in PR they don't rent.
Expert:  Doug replied 10 months ago.
Sounds good. Luckily they are usually pretty cheap. Auto stores and tool places like Harbor Freight usually have them for $10-20.
Customer: replied 10 months ago.
I rented one at autozone. Should I also remove the fuel pump fuse I read somewhere?
Expert:  Doug replied 10 months ago.
Its easier to just unplug the injectors.
Customer: replied 10 months ago.
https://m.youtube.com/watch?v=ovvXnd7AhiU
I saw this video on how to do it. Is it correct? Now I understand the 4 revs thing
Expert:  Doug replied 10 months ago.
Yep
Customer: replied 10 months ago.
This are the spark plugs look.
Customer: replied 10 months ago.
This are compression readings. What could be the problem?
Expert:  Doug replied 10 months ago.
Thanks.Two issues.... first off, the plugs look pretty rough. That orange is a low of blowby getting past the plugs, a sign those plugs are not that new.Second, and more importantly... the compression is bad on cylinder #4. This is likely why you aren't seeing any response from the EGR activation either, as when you open the EGR valve it is allowing combustion remains from cylinder #4 into the intake to re-burn... but with that low of compression (remember it is only meant to run remotely normally at 151 psi and up, and never more than 14 psi variance) there is likely sufficient unburnt fuel in the exhaust to prevent it from stumbling when the #4 exhaust is recirculated.At this point you are going to have to address the compression issue. This is what I was talking about earlier with regard to another issue impacting your EGR results.Your low compression is going to be either a result of ring wear on the piston, cracking/warping of the head, weak head gasket, or valve sealing issues. Most likely it will be valve sealing issues.To go further you will need a professional shop to do a leak down test to determine where the pressure is coming out (this requires a special tool that can not be rented usually, requires a compressor, and the tool itself is a few hundred dollars. Basically, not a DIY job). If the pressure is being lost into the crank case, then a rebuild is in order. If it is lost in the head (gasket, valve, etc), then pulling the head will be in order to send it to a machinist to check for cracks/warps and more than likely end up either regrinding/replacing valves or valve seats on #4.
Customer: replied 10 months ago.
Just to be clear. I did this test left to right. Like in the picture I included. I don't know if that's the correct cylinder numbers. I just assigned them.
Expert:  Doug replied 10 months ago.
That is correct, cylinder #1 is always the one nearest the belts, and in a four cylinder engine they are numbered sequentially, so number 4 is the far right (transmission end) in the picture.
Expert:  Doug replied 10 months ago.
I am stepping out on break for about an hour, but if you have further questions/clarifications I will back shortly to address them.
Customer: replied 10 months ago.
Can the timing belt cause low compression?
Customer: replied 10 months ago.
Also I should not run the car like these?
Expert:  Doug replied 10 months ago.
Sorry for the delay. Yes, the timing belt could cause low compression, however the problem with this is that the piston alignment is the same on cylinder 1 and cylinder 4, just with reversed valve timing. So this means if the timing belt was off a few teeth to cause the compression drop, the compression drop would be identical on cylinder 1 as it is on cylinder 4, and this is not the case in your situation. That is how we can safely rule out the belt as a prospect.You can run the car this way, it is not ideal but it isn't going to lead to any other damage as long as it isn't a head gasket causing the loss of compression... and that is unlikely since you are not mentioning any over heating, any oil/coolant mixing, or anything like that.
Customer: replied 10 months ago.
Alright. And no it has never overheated and it isn't mixing coolant with oil
Expert:  Doug replied 10 months ago.
Yeah, far more likely you have a valve issue. This is particularly common on cylinder #4 since it burns leaner when EGR operates. And in that case you can drive it... it just won't have the smoothness/power it once did, meaning you might see some loss in fuel economy. No further damage though.
Customer: replied 10 months ago.
I ask because I'm a college student and I need to travel to college daily and I already told my mechanic that when he has a spot available for my car to tell me so we can know what it causing the lost of compression.
Expert:  Doug replied 10 months ago.
Yeah again without any signs of head gasket related issue (no over heating, no oil/coolant mixing, no plumes of white smoke etc), it is highly likely to be a burnt valve/valve seat. At that there is no harm in driving it; and even if it were ring failure, still no harm in driving it. Same thing, just lower compression means lower power/rougher running by a little, slight drop in economy. It may continue that way for thousands of miles in many instances without ever changing condition.
Customer: replied 10 months ago.
That's probably why I was experiencing rough idle and occasional stalls?
Expert:  Doug replied 10 months ago.
Yes, any time you see more than 14-15 psi variance between the cylinders this causes an uneven running condition... think of the engine turning like a big circle, and each cylinder is a 1/4 pie wedge. Then picture one 1/4 wedge is smaller than the other three, if you roll the wheel it will have a noticeable "clunk" to it preventing it from rolling smoothly. The same thing is happening here; the engine expect each cylinder to fire smoothly, and you have one that is severely underperforming. This results in an imbalance causing the rough running at idle and under the right conditions (usually right after slowing down etc) it can cause a stall too.
Customer: replied 10 months ago.
That's exactly what the car did the first time in stalled. Right when I stopped at a light it did it.
Expert:  Doug replied 10 months ago.
Yeah that is when it is going to be most prone to stall. If you give a tiny amount of gas pedal when you approach a stop it will improve that condition.