Question about idling problems

[juntjoo]

What is happening exactly in the engine when, as I can describe it, while the car is idling it it seems to skip a beat or hesitate and letting off the pedal the engine struggles to catch itself from the drop in rpm's. It's obviously weaker but i'm wondering if it's not getting enough air(rich?) or the other way around or what. I'm just trying to understand how this works. BTW currently this happens mostly when the engine is under extra load from the AC or even the little rear defrost button. Really?

 

[juntjoo]

Let me pose this question: what part is responsible for keeping the engine alive after you release the pedal? The ISC correct? It gets signals from the ECU to open the throttle a little so is it not doing it fast enough and causes the engine to choke before it gets air into it? Or is it lacking fuel, or would the engine have to be hesitating while gas pedal is pressed? I'm not sure if it does that. So what exactly causes it to struggle like this and especially under AC load?

 

[juntjoo]

Yeah, why does a car struggle to idle smooth when the AC is on? Could the AC compressor be broken and be adding extra resistance? I can feel the engine really struggle when I turn it on.

 

[gmtech121]

i would start by cleaning the TB. there should be a small passage by the throttle blade for air to flow thru at idle

 

[juntjoo]

I used a good amount of carburetor cleaner to clean the TB, which I also used to spray around the injectors and TB to look for leaks. Same problem mostly with AC on. Now no cold start. Have to manually(with pedal) keep engine from stalling for about a min before it can idle on it's own.

 

[NHerron]

The TB needs to be totally clean, mainly the passages
Set the TPS to correct settings
Check ignition wires / plugs / plug gap
Boost leak test

BISS (relates to ISC) adjustment should only be adjusted with everything else is completely in spec

 

[mikesx4911]

I would do this

1. Check for vaccum leaks

2. Clean throttle body

3. Try cleaning/testing IAC this controls the idle of the car
(had a problem before when you let off the gas after a hard acceleration rpms would drop down to almost 0 and than shoot back up if I'm lucky to normal idle.

 

[juntjoo]

I would do this

1. Check for vaccum leaks

2. Clean throttle body

3. Try cleaning/testing IAC this controls the idle of the car
(had a problem before when you let off the gas after a hard acceleration rpms would drop down to almost 0 and than shoot back up if I'm lucky to normal idle.

did that solve your problem?

 

[mikesx4911]

did that solve your problem?

Yes it actually did, the shitty part about it. I took it to a mitsu dealer first because I didnt want to troubleshoot it, a day after getting it back from them and paying 300 buxs the car was dieing out again . So I said you want something done you do it your self, I found a couple of boost leaks, one being my throttle body needed to be rebuilt, it was losing air from the idle screw. I didnt feel like testing my IAC so I bought a new one on rockauto for close to nothing, figured mine was old anyway. Than my car ran like new man, I didnt get crazy ass rpms jumping around .

 

[juntjoo]

Check this out...


http://www.youtube.com/watch?v=8YXPlUQfT34&feature=youtu.be

After that it runs pretty good I think, but then I turn on the AC and it's almost inoperable.

 

[NHerron]

Have you checked the ISC coils for correct resistance and is it plugged in?
http://www.youtube.com/watch?v=KibYz21IMA0\

Do you have any CEL's

 

[juntjoo]

Is there a way to merge this thread with this

www.dsmtuners.com/forums/maintenance-repairs/437088-how-read-rpms-multimeter.html

one? If not, that is where I am and as far as checking resistance, I will try again but I think I was having problems doing that, either with the multimeter or just knowing what I was doing. At the moment I'm checking out the ISC before I check the timing.

Oh, and no CEL's.

 

[juntjoo]

Update: just re-cleaned the TB. Last time I just sprayed it. This time I used a rag and dug and I believe it made a difference, since the 1st cold start was flawless. Issue with AC almost stalling the engine still exists. Will continue(around busy work schedule) to trouble general idling issues. Thanks for replies...

And resistance good on ISC.

 

[juntjoo]

So I'm back at it again and I never solved this problem and it's still the same: engine struggles to idle especially cold or with AC on.

So I thought I'd grab a brand new ISC(apparently you can get them at your local AutoZone for $80 instead of $160 off the internet), and just like the used-but "tested good" ISC off Ebay it failed the 6v battery test and and the test where you turn the ignition one step, and it only jiggles. BUT again, just with the used one, upon turning the car on right after installing the new one, it seemed to know what to do and it revved high as it was really cold but then once I started driving same problem -struggled hard to idle. So it's not the ISC then.

What does it sound like is going on? Bad signals from the ECU? Why did it work initially? Did the ECU respond to a new ISC installed or is that how ISC's behave brand new or what? I never found any vacuum leaks? What do you guys think?

 

[triston2469]

Well I know you are supposed to let the car Idle for about 10 min after changing the ISC so it can learn the idle of the car. Also have you checked your TPS? When i bought my car the idle was all over the place and I found that not only was the ISC bad but the TPS as well as my MAS was also bad. Just hope your not as unfortunate as i was.

 

[juntjoo]

Thanks Triston. I think it's good but I'll double check. so do I remove then reinstall the ISC then?

 

[triston2469]

I wouldnt think you would have to remove. I think at this point the easiest way to go about doing it would be to disconnect your negitive battery terminal for 10 min and let the comptuer reset.

 

[NHerron]

Have you done a boost leak test yet. If theres a leak after the TB you would have idle surge.

 

[triston2469]

well i doubt its a boost leak being that his car is a N/T, but maybe a vacuum leak?

 

[NHerron]

Guess I should have clarified haha. Thats pretty much what I meant, to test for vacuum leaks somehow.

 

[juntjoo]

Nah, I can check again but last I checked vacuum was good

 

[juntjoo]

Okay just checked my records and apparently I measured 15hg where specs call for 17-22. And I remember not finding any leaks at the TB or IM. so what's next? EGR? I think that was what I was going for next before getting distracted.

I should point out I remember doing a lot of things but i'm new at it still so a lot of times i'm confused about the results.

 

[Lou98GSX]

try turning your biss screw out a 1/4 of a turn .also make sure your valve timing didn't jump a tooth that would give you a low idle.

 

[kleenf4i]

Yep defiantly a boost leak. I would say vacuum leak,maf sensor, or iac. Clogged throttle body could be the case but unlikely in this event.if the car runs fine.then rule out the maf.then it's vacuum or iac. Like said before, try to manually adjust the idle, see if it helps.
Forgot to say....when the car has ac on its a secondary symptom as to why it's bogging down.when you kick the ac on the engine needs to rev up about 100rpm, to maintain good idle.if the iac is not working or there's a vacuum leak, you will get a stalling engine because it was never idling correctly in the first place.

 

[juntjoo]

try turning your biss screw out a 1/4 of a turn .also make sure your valve timing didn't jump a tooth that would give you a low idle.

Check check