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

[Timothy Salomon]

That should be right. A few seconds should be enough to test the motor without burning it out. The link “College Man” posted on the other thread indicated the ground should be modulated, or turning on and off rapidly.

[Galant]

Alright so did the tests, one of my iac didnt move at all. The other 2 just vibrated and moves a little bit up and a little bit down. By “a little bit” i mean very tiny movement thats hard to even notice.

I believe its suppost to extend all the way out and all the way in depending on which way its jumped right?

1-2-3
4-5-6

when i jumped pin 1 and 2 i think it vibrated for a second and moved i believe up a little bit then stoped(didnt fully extend i dont think)

then when i jumped pin 4 and 5 it did the same thing but i believe it went in an opposite direction and stoped.

So none of my iac’s fully extended in or out when jumping them with the same car battery(out of the car of course)

so im going to conclude that my pcm is good, wiring is good, and its just my iac that i need to service. Yes or no?

[Timothy Salomon]

I think the more circuits you make, the further it should move. Still, if the valve is not new, it sounds like it might need to be replaced. Were the two that moved new parts?

[Galant]

2 of the iac that actually did something were old ones i had laying around. The new one i got back in February while i was still building my engine was the iac that didnt do anything at all when jumped.

1-2-3
4-5-6
Oh wait i was touching the positive wire to 1/4 and the negative to 2/5 would that make a difference?

Edit: i tried it with positive to 2/5 and neg to 1/4 and got same reactions…

[Timothy Salomon]

positive needs to be on 2 or 5 or both. you can try different ground pins for the negative side. Maybe we can get them to work?

[Galant]

i just tried with it the positive and got same result. I really appreciate the help i ordered a replacement of the new sensor i recently got and will see if that sensor works out. If not then either im not jumping the sensor right or the new sensor is bad aswell. The battery is 12v so i cant see why else the motor wouldnt move when jumped

[Josh]

http://www.ericthecarguy.com/faq/solving-automotive-idle-problems

[Timothy Salomon]

while you are waiting, you might try putting one of the old valves on your car. What if it works?

[Galant]

well i did that and the car finally started without having to hold the throttle down. Which makes me pretty sure its an iac issue because when the throttle is closed it wouldnt start and stay on meaning the cars lacking air.

The car idles pretty well in neutral and park but does jump around a bit. starts at like 1500 rpm and drops to around 700 when the engine is warmed and my car is suppost to idle 700 +-100.

So when i put it in drive/reverse the car rpms drop and tries to go back up but stalls. This tells me its something with the iac because thee ste throtte was cosed the whole time and it idles fine in neutral/park. However when it goes into drive/reverse the iac isnt moving fast enough or extending/retracting enough to catch the idle after putting load on the engine(putting it in drive/reverse). I was able to turn the heat and ac on while it was idling in park and that diddnt have much of an impact as well as turning the steering wheel.

I noticed when i have the iac out and cylce the key on and off my iac barely moves in or out. One of them doesnt move at all.. So i’m thinking because the iac is able to move a tiny bit it can handle park/neutral flunctuations. But because it doesnt extract/retract as much as i would think it should be thats why it doesnt catch the idle when i put the car in drive/reverse.

I think something in the iac is stuck or a coil is bad maiking the iac motor range restricted and or slow.

[Author]

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