If you own a 4th or 5th generation Honda Accord for long enough you'll eventually encounter some form of an idling issue.

My 1991 Honda Accord LX has surging idle when driving at night for years and I could never figure it out, even after watching many videos and trying different fixes. Then, due to major oil leakage, the car sat for 14 months before I got around to changing the leaking camshaft seal (sprocket side). Now it's back up and running and the surging idle has returned. But for the first week of driving after the car sat for so long there was no surging idle; it idled normally. Then, the idle started creeping higher each week with no surging. Eventually, the idling was high enough at around 1600 RPM that it would then suddenly drop and then quickly rise; surging, and once it gets to this point the surging stayed. Remember, all this abnormally idling only with headlights set to on. When the headlights are off the idling is constant and on the low side...so idling is affected by the electrical load on the car.

Note: the alternator charges the battery at 14.2V during idling.
I've given up on this time and again...I've just been putting up with it

Anyone out there encountered a similar situation?
-=_Dave

 

Not specifically like this, but all idle issues center on the Idle Air Control Valve (IACV). Mine was fouled with carbon, so it would randomly stall. Cleaning it helped but the C27A4 OBD2A ECU needed a fresh start and to relearn the adaptive map files (battery disconnect followed by several trips).

Your issue is correlated to the charging system. Headlamps pull from the battery through the fuse box, ECU and the Alternator can "see" this via the Electronic Load Detector. Alternator responds by increasing output (you can hear it), ECU compensates for the load with an idle response.

I suppose if there was an intake leak, the IACV would have a hard time finding the appropriate idle point. I suppose if the IACV was also carbon fouled it would struggle to hold the correct idle for the load, possibly even surge or choke.

I would clean the IACV and check for intake leaks, any way extra air is getting into the engine in an unregulated or unexpected way.

 

Some say that a vacuum leak in any fuel injected engine past the MAF or MAP causes higher RPM as the oxygen sensor compensates for the lean mixture by telling the ECU to inject more fuel to keep the air fuel ratio optimal. In this case, I would expect a vacuum leak to always cause high idle. In my case, the high idle only happens when the alternator has been loaded good by powering the headlights and all the other lights that come on when night driving. I would think that the IACV may be faulty but I put in a new one 6 years ago chasing this idle issue and it didn't solve it. It's almost as if the IACV is overcompensating and not adjusting the RPM to meet the variations in engine load when, in this case, the alternator is asked to put out more electricity...the more an alternator has to work to produce more electricity the harder it is to spin it by the crankshaft.

Sometimes I wunder if there isn't enough power for everything when the headlights come on and that somehow throws off the ECU causing high idle and idle surging.

-=_Dave

 

I pulled out he ECU under the passenger carpet and tested the capacitors with an LCR meter in circuit and discovered that 6 of the 7 electrolytic capacitors are significantly degraded.
I'm going to replace them and see if that solves the erratic idling problem.

Wish me luck,
-=_ewald

 

I didn't respond at first to this thread because the "issue" only happens with an increased electrical load.

I will add that for all idle issues one should check the PCV valve in the top of the valve cover. A missing check ball or spring will cause idle issues along the vaccuum leak motif. I would check this always as it is quick and easy to do.

It has also been my experience that if the alternator is making a lot of noise with increased electrical loading (not bearing related,) the diode bridge probably is at fault. One or 2 diodes may not be working of the 3 even though it is still charging...... Whether or not this causes an idle issue is anotrher matter beyond my experience.

And lastly, an old technician told me to use some WD-40 or Zep 45 after cleaning the air passage around the throttle plate to lubricate the moving parts. It has helped me one time before. Good Luck!