Rough idle DIAGNOSING

[Galant]

hello hows everyone doing?

I got a 2000 mitsubishi galant es 2000 v6(3.0L)

I went through hell with this car and being that im not a mechanic i replaced part after part thinking ill fix the car…

Well the car still has problems and im running low on my budget.

The problem with the car is it will stall and or have a rough flunctuating idle 0:

I hooked up my obd2 reader and looked at the live data. With the car TURNED OFF My tps which is new reads 0.0 without my foot on the throttle(gas pedal) and 89.0 with foot down fully on throttle.

I pressed slowly and released slowly on the throttle going through every number making sure there arent any dead spots in the tps 8)

Ok so what i did was i start the car and kept my foot on the throttle (my obd2 read about 3.7 for the tps) and the car idles fine no stumbling or flunctuating just perfect.

However when i lift off the throttle slowly obviously the obd2 scanner tps readings drop however the cars idle starts running rough and jumps a bit. The closer to zero the obd2 scanner reads for the tps value the rougher the car idles and rpms jump. But let me put my foot back on the throttle and anything around 3.0 for the tps reading will make the car idle perfectly.

So im analyzing this as im not a mechanic its not easy to understand. I did some research and have some questions.

1)when a cars engine is off should the tps reading be 0.0?

2)when a cars engine is on should the tps reading be 0.0?

I read about the tps suppost to be 10% of the max reading which in my cars case is 89.0 but im no mechanic so im not sure if thats true.

I also suspect that if the tps reading is relevant to the throttle plate opening degree then if the throttle plate is fully closed then the tps is 0.0. When i press on the throttle the plate opens allowing more air into the engine making the idle react normally.

So im coming to the conclusion that something isnt doing its job. And that the something that isnt doing its job is suppost to be allowing air into the engine when the throttle plate is closed(0.0 tps reading).

But then again i heard that the tps is suppost to be 10% of the max tps reading(89.0). I can get the car to idle perfectly when i press the throttle to a reading of average 3.0 or higher. So if its suppost to be 10% then what is suppost to make the tps reading go to that 10% without me pressing on the throttle?

I could extend the tps making the tps reading a steady 10% since the tps reading is based on the degree of opening of the throttle plate. BUt that would make my car take off faster and idle higher then its suppost to right? Or maybe the car is suppost to be 10% at all times even when the cars off?

IDK please help me =p im noob

Topic

[Galant]

Also im pretty sure i dont have a vacum leak considering the car idles low and or stalls when my foot is off the throttle. So if anything the car is lacking air being why it idles perfect when throttle is pressd down. But then again im no mechanic so please help

Also the maf reading on my obd2 scanner was flunctuating so im pretty sure that means the maf is good. so whats up with this

[Timothy Salomon]

Do you get voltage to the idle air control valve when the throttle is closed? If you have a mechanical throttle linkage and idle air control valve on the throttle body as I expect, it is possible the IAC valve isn’t opening.
Another problem with vacuum leak like symptoms can be caused by the egr valve.

[Galant]

thanks for being the only person who replied despite the 38 others who viewed this post.

My scanner ready in absolute tps percentage.

I belive 0.0v = 0% and 5.0v = 100%

My absolute tps percentage maxes out at 89.0% at WOT

and with my foot off the gas pedal it reads 0.0% which is when the car stalls

This is a throttle cable connected to the throttle body to open and close the butterfly valve. I have tried multiple IAC valves so i dont think its that. And changed the egr too.

I saw on a youtube video the tps is always suppost to be 0.5v and with my scanner the tps percentage reads 0% so i think i need to get the tps to read 10% which would be equal to 0.5v. No matter how much i turn the tps it will remain at 0% so im thinking i will have to adjust the throttle close screw until i can get the tps to get enough resistance to rise the absolute tps percentage to about 10%.

Am i right? My throttle stop screw is un calibrated? FOr whenever i move the tps around its not getting any resistance so the absolute tps percentage remains at 0%. ANd the only other thing that can affect the tps aside from the throttle cable is the idle scew. Please someone confirm or deny this

[Timothy Salomon]

The throttle adjustment screw should be holding the throttle open by 1/4 turn past contact just so it doesn’t get stuck.
Seems like the TPS may have a separate idle adjustment, or is it a second component?
http://www.dsmtuners.com/threads/differant-tps-adjustment-methods.103936/

http://www.dsmtuners.com/threads/throttle-body-install-question.332674/#post-151826306
I think the screw on the throttle body is only a part of the adjustment, moving the switch in and out is the other part of the process.
But by all means try adjusting the screw first.

[Corey Mason]

I would wisely guess either the IAC is bad or you do have a vacuum leak. With a runner up possibility that the throttle body needs to be cleaned.

If you car idles rough when there is NO throttle, but runs/idles well when there IS throttle….that is an indication of vaccuum. Because, when there is no throttle, the engine isn’t sucking in. When you have throttle, the engine is sucking in hard…essentially creating a major vaccuum and basically ignoring whatever vaccuum there is.

IAC is good to check because these directly work with the idle speed.

Your throttle body could help by being cleaned. If you clean it…take the blade out completely. Clean it, and the body then put it in.

You shouldn’t change or adjust the idle screw…but maybe you already did, or somebody else did. Adjust this as your last case scenario. Your car should idle in the ball park of 650ish (all cars vary).

Fuel trims would help you see if you have a vaccuum leak…if you know-how to read them.

Sent from my XT1254 using Tapatalk

[Galant]

thanks for reply.

Long story short the absolute tps % on my scanner shows 0.0% regardless of the tps sensor voltage output. SO i hooked up my multimeter to the tps and adjusted it to .50V. Now car wont even start unless i put my foot on the gas and it wont idle unless i press the gas open.

Im guessing this is because the engine is lacking air when the throttle plate is closed. Opening the throttle screw and closing it fully seems to have no impact on getting the car to start without pressing on the gas pedal.

So im suspecting the iac since i belive it to be the only other device that allows air into the engine that controls the idle.

So i tested the harness of the iac and its getting the 12v and i tested the ohms which all checked out on the iac sensor. IDK how to test the pcm signal wire on the iac to see what the demands are…

But i did notice when i took the iac out the TB and turned the key on and off the iac just vibrates basically for half a second. IT doesnt move fully down and up like i see in youtube vvideos of other people doing the test. But the iac does have the proper ohms readings so whats the problem you think?

[Galant]

bump

[Timothy Salomon]

This diagram suggests the IAC may have 2-3 power feeds if it is a 6 pin connector. It should get a ground to turn it on from the ecm. Probably 2 12 v inputs, and a 5v monitor with signal or control going back to the ecm. Not sure which wire controls the actual solenoid. You might try unplugging the valve and trying 12 v power with a jumper wire to see if it functions normally. If it works, you might have a weak ecm ground or too much resistance in the wire.

Attachments:

• Screenshot_2016-05-03-22-48-42.png

[Galant]

1-2-3
4-5-6

2 and 5 above give 12v

3 and 4 give 0.15v

is this normal?

[Timothy Salomon]

If this is correct, you should get grounds on the terminals 1,3,4 & 6.
http://www.club3g.com/forum/maintenance/140906-how-testing-iac-idle-air-control.html#/forumsite/20491/topics/140906?page=1

That probably explains almost no voltage on pins 3 & 4. Try testing these from one of the powered pins using a pin to backprobe the connector while the IAC valve is plugged in. The car should provide more grounds as idle speed drops and less grounds as it increases. You should read a full 12 v on the working grounds, if not you need to check for continuity to the computer and any of its grounds. I wouldn’t expect .15 v to operate the IAC valve. Test again to try to verify the poor connection to the computer and look for wiring harness integrity.

[Galant]

how do i test it ?

1-2-3
4-5-6

2 and 5 are 12v when the key is on and 3 and 4 are .15 aswell

so i should backprobe the pin(3) and connect the positive wire there. And connect the negative wire to the battery negative terminal?

Then start the car and watch the voltage at idle ?

[Galant]

new question

1-2-3
4-5-6

so 2 and 5 are 12v when key is on and i connect my mutimeter to neg battery post and other to iac harness pin 2 and 5. when i connect my multimeter positive to the battery positive post and my multimeter neg to pin 1 and 6 it reads 12v when i tried connecting to 3 and 4 it read 0v and this is also when the key is on.

So my question is should pins 1,6,3,4 all read 12v when i connect my neg multimeter to the battery and postive multimeter to each pin? or is it only suppost to be pin 1 and 6 that read 12v?

[Galant]

bump —

[Timothy Salomon]

I think all 4 pins, 1,3,4,6 should show 12v with the multimeter connected to battery positive, but the engine must be running, so the computer can determine how many of the circuits should be operating. if some of the pins have a good ground, 1,6 the valve should be at least partially opening. You might be able to confirm this by unplugging the connector and using jumper wires to connect pin 2 to battery positive and either 1 or 6 to battery negative for a moment to see if the valve opens.

[Galant]

1-2-3
4-5-6

so connect 2 to the positive battery and 6 or 1 to negative battery and see if the valve opens. I can do this with an extra car battery and the iac out right?

To test if it closes i connect positive to pin 5 and negative to pin 1 or 6?

[Author]

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