marzubus

Since the last 7 years, I have had what started out as intermittent rough idle issues, when the engine just sometimes idled about 200 rpm lower than normal, eventually it escalated to it being permanently "rough" idling for the last few years. I had ruled out many things over the years from battery, to coil packs, to IAC valve, the MAP sensor, the cables to the MAP sensor. Spark plugs, bad fuel. Nothing improved the situation.

The last year the engine was running really rough at idle, often cutting out when I would press the clutch in at a stop, resulting in me braking, while throttling to keep the engine alive, or popping the clutch when it died to restart the engine, but then something changed, and the engine started running rich in addition to the rough idle. Honda still could not say why it was running rich, so they wanted me to pull the fuel tank, and inspect / clean the tank. But its a huge job and very expensive.

So I drove the car very little while it was running rich, as its not good, but driving it did pay off, as the rich fuel mixture eventually unmasked the culprit, when the Check Engine light came on.
The code: the front O2 sensor, after replacing the sensor, everything is as it should be. Idle is good, Engine is good. No more miss fires, no more rich smell, idle is good. All is good!

TL;DR: chronic rough idle was caused by front O2 sensor: 36531-PCX-014

2004 S2000 AP2

engifineer

I think you mean O2 sensor.

I would avoid that honda dealer for anything but buying oil filters by the way



And I have never in my life heard of cleaning a fuel tank to try and fix a rich condition.

cgarrett23

I thought that was odd as well. Typical Honda dealer BS.

Car Analogy

Kudos to you for posting to add to the rich knowledge base here!

It might be helpful to state which generation your car is, ap1, ap2, or dbw, as there are differences that could matter in how symptoms would manifest.

marzubus

good point, added it to the end of the the text body.

yourboysoap

incredible that honda dealer would resort to pulling a fuel tank before even thinking about the reason cars usually run rich, in an o2 sensor. glad you found it! i had long term issues myself and it ended up being one of the ignition coils was arcing. replacement fixed it.