IACV Problems

[Malo 809]

Hi All, I just purchased a 1998 Honda Accord LX Coupe with a 2.3L 4 Cyl 5 speed manual transmission at an auction. The car has 159K miles on it. This will be my daily for the foreseeable future so I need to get this thing in good running condition ASAP. I’ve fixed a bunch of problems already but I have one main problem I can’t seem to fix.

The car had a bunch of codes all of which have been cleared except for this P1519 IACV Circuit Failure code. Along with the code I have a fluctuating idle between 1200-1400 RPM, assuming the two are related once this is fixed I should be good to go. (Side note at idle exhaust really stinks which I believe means I’m running lean which I also believe could be tied to this IACV problem because the AF ratio is off). After some quick research I came across this site with some troubleshooting steps.

Initially I tested the circuit and had a good solid ground connection on pin 3, steady battery voltage on pin 2 and 6-7 volts on pin 1, all checking out right? So I move to the valve. I removed it from the car and checked the resistance as per the troubleshooting steps. The Ohm readings were way out of range, so bad part right? I run to the local parts store and $160 later I’m back with a new part, I check the Ohm readings as per the troubleshooting steps and bam 10 OHMs on the nose so all should be good. I install the part hook up my coolant lines test everything, top off my coolant and crank the motor. The code is still on and he motor still has a fluctuating idle. So I go back under the hood, pull the connector and test voltage again. All the numbers are still adding up. What else can I try? I’m starting a new job tomorrow and it’s a 40 mile commute, I would really love to have the car running in good condition before then.

 

[Malo 809]

I had a friend suggest checking/replacing the MAF sensor, I'm skeptical but at this point I'm willing to try anything. Going to try that tomorrow morning. If anyone else has some insight or suggestions, PLEASE HELP! Much appreciated.

 

[BlkCurrantKord]

These cars don't have MAF sensors. Did you burp the cooling system to remove any trapped air? You have/had an air leak somewhere.

 

[Malo 809]

Yea when I refilled the coolant after installing the new IACV I did burp the system.

 

[Malo 809]

So I have an update. I found the service manual for my car and there are some troubleshooting steps for this particular issue. Steps include testing the IACV plug for battery power, ground continuity and the signal wire from the PCM to the connector. All check out down to the last step which says to plug in the IACV, switch the car to on and check the signal wire at the PCM end of it for voltage. It asks if there is "battery voltage" which to me means 12.4 V that I'm getting at the battery right? The reading at the PCM is 10.2 V.

Would the loss of 2V account for this issue? The next steps in troubleshooting say if there is battery voltage to replace the PCM with a known good working one and test again if no, replace the IACV.

Any suggestions? If it's the PCM I'll probably try to order one on eBay, I'm seeing some for $90-100 with warranty.


.....giving up hope on finding help here -_-

 

[Eclipse99fwb]

Its not as active as it once was on here, still alot of good people who will try to help. On monday i will look up the code at work and all steps to check. I have seen low voltage cause all kinds of wierd issues, good chance it might be the cause. On a side note the fluctuating idle happen to me the other day where the car would rev up to 1200-1500 on its on while idling, no codes though. Stopped when i shut the car off and restarted it. Hang in there and keep up to date on your progress. Also alot of factory codes call for replacing the pcm with a known good unit to rule it out, at my shop that is usually the last step as they dont go bad often. I cant even recall ever replacing one on a 6th gen unless it was obviously bad like from water intrusion.

 

[Eclipse99fwb]

Here are some things you can check in the meanwhile, use carb cleaner with the engine running (do not spray the exhaust and be safe have a fire extinguisher with you) and spray around the vacuum hoses, intake manifold. If you notice a change in idle than you have a vacuum leak. Im sure you checked the iacv connector for corrison when you tested voltage and ground but incase not check.
Also i know you just replaced the iacv but you may want to double check it is not defective. Just provide a 12volt power and ground to the right pins make sure you hear clicking. Another thing to check is your throttle cable (what i suspect my issue is) make sure there is slight slack with the throttle closed as you are around the same mileage as my 98. Make sure your throttle is closing and not sticking but not wedging shut. Last but not least check your brake booster vacuum hose, i had a civic a year ago same problem but his hose had a tear and would cause a idle surge when pressing the brakes.

 

[Eclipse99fwb]

Also you should let the ecu relearn its idle after you check for leaks, throttle cable, etc.
Fix problems first:
- find & fix any vacuum leaks
- clean the throttle body bore & throttle plate
- clean the IACV (skip since you replaced and if you know it is activating by testing solenoid like i mentioned above)
- make sure the throttle plate closes completely
- - (mechanical stop-screw is only used to prevent it from wedging stuck closed)
- make sure the throttle cable goes a bit slack
- - (throttle cable is never used to adjust idle)
- make sure the cooling system has no air pockets (they confuse the system) should be okay since you bled the system but never hurts to do again.

Find the parts first. (For anyone else in the future)
- Idle-Air Control Valve (IACV) is usually bolted to the back of the intake manifold
- Idle-Air bypass screw is just above the throttle bore, recessed in a hole in the throttle body, it's usually a brass screw with a straight slot for a screwdriver

Procedure:
- Warm the engine up completely.
- Turn off all loads (AC, blowers, defoggers, stereo, EVERYTHING)
- Unplug wire harness from IACV (engine will almost stall)
- Adjust the idle-air bypass valve for 550 RPM (keep in mind the first notch after 0 on our tach is 500rpm not 250)
- - (PLEASE anyone with specific RPM for certain years chime in)
- Turn the engine off & plug everything back in

Now you should force the system to re-learn the idle behavior:
- Allow the engine to cool down completely
- Reset your ECU (different years pull various fuses) i cant remember the exact fuse on ours but i know its in the fuse box on the passenger side dash i think its the clock fuse.
- Start the engine without touching the gas pedal
- Allow it to run & warm up completely without touching the gas pedal

 

[Malo 809]

Also you should let the ecu relearn its idle after you check for leaks, throttle cable, etc.
Fix problems first:
- find & fix any vacuum leaks
- clean the throttle body bore & throttle plate
- clean the IACV (skip since you replaced and if you know it is activating by testing solenoid like i mentioned above)
- make sure the throttle plate closes completely
- - (mechanical stop-screw is only used to prevent it from wedging stuck closed)
- make sure the throttle cable goes a bit slack
- - (throttle cable is never used to adjust idle)
- make sure the cooling system has no air pockets (they confuse the system) should be okay since you bled the system but never hurts to do again.

Find the parts first. (For anyone else in the future)
- Idle-Air Control Valve (IACV) is usually bolted to the back of the intake manifold
- Idle-Air bypass screw is just above the throttle bore, recessed in a hole in the throttle body, it's usually a brass screw with a straight slot for a screwdriver

Procedure:
- Warm the engine up completely.
- Turn off all loads (AC, blowers, defoggers, stereo, EVERYTHING)
- Unplug wire harness from IACV (engine will almost stall)
- Adjust the idle-air bypass valve for 550 RPM (keep in mind the first notch after 0 on our tach is 500rpm not 250)
- - (PLEASE anyone with specific RPM for certain years chime in)
- Turn the engine off & plug everything back in

Now you should force the system to re-learn the idle behavior:
- Allow the engine to cool down completely
- Reset your ECU (different years pull various fuses) i cant remember the exact fuse on ours but i know its in the fuse box on the passenger side dash i think its the clock fuse.
- Start the engine without touching the gas pedal
- Allow it to run & warm up completely without touching the gas pedal

I didn't get alerts to this post, just seeing this now. I went ahead and bought a used ECU from ebay for $60 and very skeptically and painfully paid a locksmith $60 to reprogram my key to work with the new ECU. A few short moments later we cranked the engine over and I heard a smooth idle for the first time, IT'S FIXED! Thanks for the input and help on this.

 

[Eclipse99fwb]

Glad it worked out, very surprised it was the ecu but you never know. Thanks for the update hopefully this will help others in the future.