IAC diagnosis

**4g63lover** · 10-15-2010, 04:14 PM

So my car has been plagued with the P0505 (Idle control System Malfunction) code even before I swapped to the V6 TB. The time has come for emissions so I'm trying to nip it in the bud (I know, I should've addressed it earlier).

Car has the V6 TB on but has the I4 gasket, haven't addressed this yet either.

Symptoms:
-High idle at start up (2k-2.5k RPM) for about 2-5 minutes
-Idle drops to 800 rpm once car is warm and after 5 minutes idle time
-Idle is normal while coasting in Neutral
-Idle is normal at start up after initial start up for the day.

What I've done so far
-I've ohmed the IAC out. The FSM says, to test with the Coolant Temp sensor reading 60 degrees and below. It does not pass the resistance test. FSM calls for 28-33 ohms of resistance and the IAC is reading 61.7 ohms.
-Physically checked the IAC (Here's where it gets interesting), and the fucker turns on! I had my little sister sit in the car and turn it to the on position without starting it as I watched the IAC. As she turns it to "on" the IAC buzzes and quits.

Thats is extremely confusing to me, is it possible for the IAC to still function even if it is out of whack resistance wise? Is the out of spec resistance enough to throw the P0505? I wanted to do a voltage drop test but the FSM doesnt say if it gets a 5V reference or Source voltage.

I've yet to clean the TB and IAC and there is no Vacuum leaks obviously present. Going to vacuum leak test to make sure.

I will update this thread as I diagnose it some more, but would like some input. I know there are a lot of threads about the IAC codes, but I felt like we didn't have a serious diagnosing thread for it.

Please feel free to share you input, it will greatly be appreciated.

**stvn_mj** · 10-15-2010, 06:10 PM

i had the same symptoms and mine still idles high for about a minute or less. I swapped both the IAC and TPS and haven't had the code come up again.

**RedGalant2k1** · 10-19-2010, 07:32 PM

Start by cleaning the IAC and TB then go from there.

**Djayfusion99_es_v6** · 10-24-2010, 02:58 AM

I have the same problem i got the v6 though i bought a new idle air servo. still same problem. cleaned the tb, cleaned maf, cleaned intake manifold, upper and lower. i also put a smoke machine too the vaccumm system and no leaks. i am going to change out the thermostat tomorrow car is running a little hot and flushing coolant. coolant temp sensor also changed the other one broke while doing the tune up. but i was reading up on it and this is what i found.

DTC set criteria
1 vehicle speed has reached one mph at least once. engine is in closed loope idle speed control. Code will set if actual idle speed is 300 rpm or more great than target idle speed.
2 vehilce speed has reached one mph at least once. engine is in closed loop idle speed control. Maximum outside temp is less than 113F. Engine coolant temp is more than 176f. system voltage is more than ten volts. Intake air Temperature is more than 14f. barometric pressure is more than 11psi. code will set if actual idle speed is 200 rpm or more higher than target idle speed for 12 seconds.
3 Engine is in closed loop idle speed control. Engine coolant temperature is more than 176f. system voltage more than 10 volts. Power steering switch is off. volumetric efficeincy is less than 40 percent. intake air temp is more than 14f. barometric pressure is more than 11psi. code will set if actual idle speed is more than 100 rpm lower than target idle speed for 12 seconds.

any help and info to help me fix this p0505 will be appreciated. thanks in advance and good luck to all who have the very annoying code.

**Djayfusion99_es_v6** · 10-24-2010, 12:33 PM

here we go just changed the thermostat and flushed coolant. cleared p0505. apparently if the temperature read out is high makes the idle run weird. then since i cleared the code flushed the system changed the thermostat the car runs awesome and not stored code and the idle leveled out so.....EVERYTHING IS GREAT. I hope this helps with this crazy p0505 code.

**4g63lover** · 10-24-2010, 01:32 PM

Might just go an try that. That makes a lof of sense.

Though, I am running a coolant bypass at the TB so results might be different.

**4g63lover** · 11-08-2010, 05:08 PM

Cleaned out the TB and IAC. The IAC resistance is now in spec. idle seems to have gone back to normal. The IAC and TB was filthy.

I will post pics later.

**beam514** · 11-08-2010, 06:29 PM

dang lol. Still all the original stuff I sent you?

**4g63lover** · 11-08-2010, 07:17 PM

yup.

Here we go.

I did some work on the car yesterday and here are the results.

First off you have to remove the throttle body off of the car to give it a thorough cleaning.

You can find the tutorial here https://www.thegalantcenter.org/showthread.php?t=38424

Anyways. So I tested the IAC with my voltmeter and it was way out of spec. Atleast the first circuit was definitely out of spec.

The last time I checked the IAC both circuits read 67.1 ohms or something like that. This time the second circuit was reading 29.8 ohms meaning it is in spec.

WEIRD.

lol.

Ok so I got to work, I cleaned out the TB with this

and I cleand the IAC, TPS, and MAF with this.

This is what the TB looks like after cleaning. I forgot to take pics of the clean IAC and TPS but just trust me when I say that the color of the spring in the IAC was total opposites of each other before and after cleaning. Same with the TB where the IAC goes.

DRUM ROLL PLEASE!!!!

And here are the resistance readings of the IAC after it was cleaned.

First Circuit

Second Circuit

Sorry about the nail. lol. I killed it on an alternator bracket putting a header on a SER SPEC V

The car runs and idles properly. Cold start chills at 1500 rpm for a minute or so then levels out to normal idle 700-800 RPM. Will record video tomorrow. Drove it around and it idles in neutral properly as well.

Hopefully this helps someone.

**o1naturalhigh** · 11-08-2010, 07:22 PM

yep, that nail looks like it's gonna fall off soon...i give it about 1 1/2-2 weeks.

**4g63lover** · 11-09-2010, 10:42 PM

Passed the emissions test. Galant has got a good bill of health! =)

**M-Rod** · 11-09-2010, 10:48 PM

Originally Posted by 4g63lover

Passed the emissions test. Galant has got a good bill of health! =)

Sweeet! Good news indeed.

**keith6110** · 11-09-2010, 11:57 PM

Originally Posted by 4g63lover

Passed the emissions test. Galant has got a good bill of health! =)

Awesome! I wasn't sure what the plan was for the IAC lol

**4g63lover** · 11-10-2010, 12:57 PM

LOL! It's all good bro.

**4g63lover** · 11-10-2010, 05:54 PM

Shitty quality video of how the car is idling now. I used my point and shoots video setting.

**IVORY_G** · 11-10-2010, 06:22 PM

I remember about three years ago I was cleaning my I4 TB with some MAF cleaner & was unaware that I needed to take out the IAC in order to clean the TB. So all the cleaner & dirt went down into the air ducts and gunked up the IAC. Then being the noobie I was I took some steel wool to the tip of the IAC. SMH, so it started the erratic RPM's and choking. Needless to say I got another IAC & my problems were solved.