The car in question is a 6th gen 1999 Honda Accord Lx with the v6 engine. The car is having a fluctuating idle issue. It also has the check engine light on. I borrowed a scan tool from a family friend and with the very limited time I had with it, it gave me the P0505. Because I had very limited time with the tool, I wrote down everything on each screen displayed by the scanner. However, I wasn’t able to gather any information about why the check engine light was on.



These are the transcripts of the pages displayed by the scan tool. The blue text seemed to be the title of the displayed page and the red text was the error code which would be accompanied with other information. The scan tool I was using was the Zurich ZR13.



[Page #1[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[

Global OBD2 Honda (Blue)



P0505 (1/2/) Stored (Red)



Idle Air Control System



DTC (Diagnostic Trouble Code) Severity 2 of 3:

Repair immediately if drivability issues are present. Threat to essential system components if not repaired as soon as possible.



[Page #2[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[

Honda OEM Enhanced PGM-FI – Fuel Injection Control Module (Blue)



14-2 (1/1) Confirmed (Red)



Idle Air Control System



[Page #3[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[

FIX-Assist® (Blue)



P0505 Honda Stored (Red)



* IAC valve circuit open, shorted to ground or to power (B+)



* IAC valve is damaged or has failed



*Fast idle thermo valve (FITV) is damaged or has failed (some models)



*Throttle body is dirty or full of sludge.



*PCM has failed.

]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]]





So based on the P0505 error code, I started searching the forum for other people’s situations involving this code. From what I could gather, the IACV may have failed, there was a vacuum leak, or other components have failed.



Before I began troubleshooting anything else, I wanted to focus on the component that the scan tool focused on. The IACV. Before I began troubleshooting that component, I documented what the Accord was doing before I did any testing.



The IACV Plugged in:

When the vehicle starts, it revs high to 2100 rpm. After a few seconds it drops down to 1300 and starts fluctuating between 1300 to 1800 RPM. This fluctuation only occurs when in park or neutral. In any other gear, the rpms drop down to 1100.



To test if the IACV was playing a role in the fluctuating rpm, I read from another forum posts that if the IACV is unplugged, the rpms should drop. Other form posts stated that the rpms should drop to 600 or something around that range. So I decided to test what would happen if I unplugged the IACV and started the car.



The IACV Unplugged:

When the vehicle starts, it revs up to 1500 rpm and stays there. No fluctuation occurs. It stays at 1500 rpm in park or neutral. When put into any other gear, it’s rpms drop down to 1200.



I even started the car with the IACV plugged in and while it was running, I unplugged it and the rpms would stop fluctuating between 1300 to 1800. The rpms would stop at 1500.



These results started to make me wonder if other components were causing the high rpms. But then I remembered reading from other forum posts that the vehicle is capable of still functioning in a way that accommodates for a faulty component even if that component wasn’t causing that issue anymore. I remember people stating that the computer needs to be reset to wipe these errors codes so that the vehicle can start relearning how to function normally again. I also remembered that my scan tool stated that these error codes were stored in the computer’s memory. Since they are still in memory, that should mean the car’s computer still thinks the IACV is faulty and the computer is still trying to make the vehicle function in a way that accommodates what it still thinks is broken.



So here is my question. Should I keep the IACV unplugged and unplug the battery to wipe the computer of it’s errors. Then test the vehicle to see if stops idling high in neutral or park?



On a side note, I took the air intake hose off to check if the throttle was stuck open because of slug. After looking it over, nothing is keeping it open and it closes just fine.

 

Check your fitv. On the 2.2s you can open it up and there is a plastic disc that loosens up, snug it back down and reinstall.

Check the Accord FAQ at the top of the page for IACV and FITV.

 

I don't think my 1999 v6 accord has a FITV. I can't find the FITV on any diagram for this Accord model.

 

Quick update, so today, when I first started the car, it had the fluctuating idle issue I mentioned at the start of this thread. While it was fluctuating I had already plugged in scan tool I previously borrowed so could watch the live data of the vehicle. As I was doing that, the fluctuating idle issue went away after a few minutes of idling. It now idles at 1100 to 1300 rpm in park or neutral. In any other gear, it idles at 850 rpm. After I turned the car off and back on multiple times, it still wouldn't have the idle issue I mentioned. However, it still has1300 rpms in park or neutral. Perhaps warming up the vehicle may play a role in this fluctuating idle issue.

Any ways, after having more time with the scan tool, I was able to look more into the stored p0505 error code on the vehicles computer. This is the live data it captured when this error occurred.
Fuel System 1: OL-Drive
Fuel System 2: N/A (Doesn't have one.)
Calc Load: 27.8%
ECT (Engine Coolant Temperature): 183 F
STFT B1 (Short Term Fuel Trim): 0.0%
LTFT B1 (Long Term Fuel Trim): -7.0%
MAP (Manifold Absolute Pressure): 8 (inHg)
Eng RPM: 2374
IAT (Intake Air Temperature): 108 F
TPS (Throttle Position Sensor): 9.8%

The service manual for my vehicle states the following about the Idle Control System.
"When the engine is cold, the A/C compressor is on, the
transmission is in gear, the brake pedal is depressed,
the P/S load is high, or the alternator is charging, the
PCM controls current to the IAC valve to maintain the
correct idle speed."

Knowing that, why is the PCM telling the IAC valve to open more out of gear, yet when in gear, the PCM tells the valve to close. One would think the PCM would tell the IAC valve to close more when out of gear so that the rpms would be lower than the rpms in gear.

I'm going to try and start the vehicle tomorrow in the morning to see if the fluctuating idle problem returns.

 

TPS should read 0%, or real close to 0% at idle. The throttle blade being partially open is causing your high idle. Look up the procedure for setting BASE idle speed for your year engine.

Aside from that, the TPS could be going out.

Also, figure out WHY the TPS is reading high at idle. Could be a bent tab near the spring, or someone "modified" the assembly before you got the car.

At any rate, the throttle blade is NOT completely closed. Figure that out, then set your base idle speed.