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Idle air control valve trouble shooting

Tiny
LUCAS BOYAN
  • MEMBER
  • 2002 HONDA ACCORD
  • 2.3L
  • 4 CYL
  • 2WD
  • MANUAL
  • 217,000 MILES
Stumped on this. Car starts fine in open loop; idle is slightly high around 1,000 rpm's (before this problem occurred it would be around 750-InSpecs). After running the car until closed loop happens the car will idle up and down from 1,000 to 1,250-1,500 rpm's. The car started throwing the code p0505 idle air control valve system failure. I checked the battery reference which is 11.69 volts for a 12v ref wire. Continuity from battery ground to ground terminal was 1.6 ohms and the signal wire has a resistance of 56.97k Ohms. I could not find a spec for the signal wire resistance. I replaced the valve and the problem still is occurring. Old valve only had continuity between pins 1-2 the new has continuity between 1-2 and 1-3. After smoking the engine (cold) the evap valve is the only slight vacuum leak however this isn’t throwing a code at all. At the same time this started happening my heat also stopped functioning. Any possible leads or advice?
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Tuesday, November 12th, 2019 AT 6:13 PM

18 Replies

Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
I just want to make sure that when you are measuring resistance that you are only measuring the wires. Meaning the connector is unhooked from the PCM to the IAC and you are measuring from wire end to wire end. The reason I ask is the signal wire resistance is vert high. You should have less than half an ohm on that wire. I suspect that is with the PCM still plugged in and you are measuring the resistance through the circuit board as well and we don't want to have that in the measurement. Measuring resistance like this is just making sure that you don't have a broken wire or a chaffed wire that will through off your voltage reading because the PCM needs an accurate voltage to know what the sensor is doing.

Even your ground is about 1 ohm higher that I would like to see for a ground so just make sure this is not measuring through the IAC.

Let me know this information and we can go from there. Thanks
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Wednesday, November 13th, 2019 AT 4:37 AM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
Yea, I was checking to see if the wires were shorted to ground. I wasn't too sure which connector to unplug and the pin identification of where b23 was on the main connector. Are you able to get me a connector diagram for the PCM harness?
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Wednesday, November 13th, 2019 AT 5:26 AM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
I was able to take a short video of the pids on a Snapon scanner. It appears when it happens the timing is being advanced by about 28 degrees.
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Wednesday, November 13th, 2019 AT 3:55 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
I gave you each of the connectors for you vehicle but for this circuit you need connect B and look at pin 23. Measure resistance from here to the IAC on pin 3.

As for the timing jumping, I am not sure that is causing the issue, it may be a symptom. Let's just make sure the resistance is good and no shorts and we can go from there.
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Wednesday, November 13th, 2019 AT 6:16 PM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
I was able to verify on the ground I had 1.1ohms of resistance. The signal wire has.8ohms and the power has.3ohms. I also have 11.6v going to the power pin.
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Thursday, November 14th, 2019 AT 6:36 PM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
Okay. The ground is a touch high but I don't think that is going to cause this issue and the others are perfect. Since that is okay, let's go back to the P0505 and jump to where I circled in red. When the engine is warm you idle appears to be over 750 and it ranges. So we need to block the lower port of the throttle body as shown and see if the RPM's drop. If they don't then you have a vacuum leak somewhere in the intake system that is pulling in unmetered air.

Here is a guide that shows how to find a vacuum leak with a carburetor cleaner. Basically you are looking for where you spray it and the RPM goes up. This is where it is pulling air in and it brings in that fuel source and the RPM will go up.

https://www.2carpros.com/articles/how-to-use-an-engine-vacuum-gauge
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Thursday, November 14th, 2019 AT 6:49 PM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
I have a smoke machine. The only vacuum leak is from the center of the EGR valve and is very small. My throttle body doesn't have a lower port either I only have the upper port that feeds into the EGR.
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Friday, November 15th, 2019 AT 5:39 AM
Tiny
KASEKENNY
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Okay. This is a 2002 Accord 2.3L? What model? DX, EX, LX, SE? I thought they were all the same but maybe not.

Can you re-shoot the video that you took with the engine running and get the data that you showed? There was a bad glare and the actual data readings were cut off so I can't see them. Just make sure you get the data when the engine is surging. Thanks.
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Friday, November 15th, 2019 AT 7:39 PM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
My car is the EX Coupe version the engine is swapped though. It is a ulev 2.3 f23A4.
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Saturday, November 16th, 2019 AT 7:14 PM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
I will have to retest the scantool on Monday after work. My throttle body only has the one port on the top.
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Saturday, November 16th, 2019 AT 7:14 PM
Tiny
KASEKENNY
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Okay. Did the issue start after the engine swap or was the engine swapped a while ago? Also, what car did the engine come out of? Model and year?
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Sunday, November 17th, 2019 AT 5:48 PM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
Same engine out of the same car. The engine has been swapped for 40,000 without any problems.
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Monday, November 18th, 2019 AT 3:23 AM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
I ordered a new IACV. Can you get me what each pin should read as tested to continuity with each other? I think the other was allowing coolant into the electricals because everything was shorted together.
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Monday, November 18th, 2019 AT 3:24 AM
Tiny
KASEKENNY
  • MECHANIC
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You mean the continuity on the IAC itself or the wiring connector? The wiring should have no continuity with each other because Pin 1 is ground, 2 is your reference voltage and 3 is your command from the ECM.

As for the valve, I am not sure. You would need to compare it to a new one because they don't give that reading and I can't say I have ever checked one that way.
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Monday, November 18th, 2019 AT 6:08 PM
Tiny
LUCAS BOYAN
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  • 17 POSTS
I got a new Known good IACV and the problem still persists after I did the idle relearn. What is next?
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Thursday, November 21st, 2019 AT 3:03 AM
Tiny
KASEKENNY
  • MECHANIC
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Okay. Just going back over all of this to see if we missed something and I didn't pick up on it prior but this ranging only happens after it goes to closed loop? If that is the cause, the only thing that changes is the PCM starts running the engine off of the engine sensors and o2 sensor data. Have you monitored o2 sensor data to see what it is doing? I suspect the short term fuel trim will be negative. This means there is a smaller amount of oxygen in the exhaust due to a higher amount of fuel and the RPM's are high. So the PCM starts to pull fuel and when it does, the RPM's drop and the exhaust goes lean (high amount of o2) and it commands more fuel and the RPM goes back up.

Maybe get a video of the RPM surging because the PCM is not going to react extremely fast but it will be pretty responsive.

Basically, with the issue happening after its warm, we need to start looking at a sensor input to the PCM.
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Thursday, November 21st, 2019 AT 5:41 PM
Tiny
LUCAS BOYAN
  • MEMBER
  • 17 POSTS
Yea the problem only happens when the system reaches closed loop. Today driving it I just got another code p1381 for the cylinder position sensor signal intermittent and the car went into limp home mode. How would I test the ECU? I am starting to believe that is the cause of these problems. Figure the ECU is 17 years old.
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Friday, November 22nd, 2019 AT 8:28 AM
Tiny
KASEKENNY
  • MECHANIC
  • 18,907 POSTS
You could be right. However, it appears the easiest way to tell if it is a wiring issue or the ECM is to clear it (reset ECM) and then start the engine. If it sets then it is most likely the ECM. If not, then you probably have a wiring issue. Here is the test that details this.
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Friday, November 22nd, 2019 AT 9:04 AM

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