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ase_master327, Shop Owner
Category: Honda
Satisfied Customers: 5288
Experience:  +15 years experience with Hondas. Bumper to bumper diagnosis & repair.
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1998 Honda accord: idle control system malfunction..warning lights

Customer Question

My 1998 Honda accord came up w/ a P0505 code; idle control system malfunction and the panel warning lights are on. Can you tell me exactly what is going on?
Submitted: 8 years ago.
Category: Honda
Expert:  ase_master327 replied 8 years ago.

Which engine?

Customer: replied 8 years ago.
Reply to ase_master327's Post: V6 3.0 vtec
Expert:  ase_master327 replied 8 years ago.

This is a malfunction of the idle control system. Keep in mind that if there is a short in this system that it is VERY likely that the computer will also be damaged. It is not uncommon to have to replace an IAC along with a computer...Anyways, here are instructions for finding out the cause of this problem on your 3.0 V6 Accord.

1. Start the engine. Hold the engine at 3,000 rpm with no load (in Park or neutral) until the radiator fan comes on, then let it idle.

2. Check the engine speed at idle with no-load conditions: headlights, blower fan, rear defogger, radiator fan, and air conditioner are not operating. Is it 700 ±50 rpm ?

YES-Intermittent failure, system is OK at this time.

NO-If the idle speed is less than 650 rpm , go to step 3; if it's 750 rpm or higher, go to step 4.

3. Disconnect the 3P connector from the IAC valve. Dose the engine speed increase or fluctuate? YES-Adjust the (base) idle speed. If it's impossible, clean the ports in the throttle body. NO-Replace the IAC valve.

4. Turn the ignition switch OFF .

5. Remove the intake air duct from the throttle bod.

6. Start the engine and let it idle


7. Put your finger on the lower port (A) in the throttle body. Does the engine speed drop?

YES-Adjust the idle speed. If it's impossible, replace the IAC valve.

NO-Check for vacuum leaks, make sure the throttle valve is completely closed, and repair as necessary.

ase_master327, Shop Owner
Category: Honda
Satisfied Customers: 5288
Experience: +15 years experience with Hondas. Bumper to bumper diagnosis & repair.
ase_master327 and other Honda Specialists are ready to help you
Customer: replied 8 years ago.
Thank you for your answer. In regards XXXXX XXXXX warning lights in the panel (ABS, battery, oil, and brake lamps), does it have anything to do with the alternator or maybe a short circuit in the electrical system?
Expert:  ase_master327 replied 8 years ago.


Anyways with the lights on, I would be really looking into the code, just for the simple fact that it is an idle system malfunction. If the engine is not idling fast enough, then the lights will come on. This is because the alternator will not be turning fast enough to charge the system creating a lower than normal voltage condition.

If the lights are on even while driving down the road, then yes...I would be inspecting the wiring or maybe even a main relay (though not the most likely cause).

The only one I am really concerned with is the battery light, so put a voltmeter to the battery with the engine RPM raisedf above idle, and check the voltage. It should be NO LESS than 13DCV. If it is, then you can start looking into the wiring or chraging system for the cause of the problem.

If you still need anything, I'll be in and out 24/7, though it may show me to be online all the time...It is only because my internet connection stays on. Laughing


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