I'm getting a misfire that occurs only rarely, but has me worried. Currently, I typically have it when accelerating under medium throttle between 3-5K rpm, and it causes just one or two stutters before disappearing at higher or lower rpm/throttle. In normal city driving, it might only happen every 5-10 minutes. Although, it's worth noting that over the cooler SoCal "winter" (45-60deg), it would also sometimes happen at narrow throttle when just starting out (i.e maintaining low speed in 1st or 2nd, with the engine still cold).

- Car is an '00 with 63K.
- There are no current or pending OBDII codes.
- ECM was replaced with a used, low-miles '03 part a few years and <20K miles ago due to a much more severe misfire issue (both the original ECM and coil packs were fried).
- New iridium plugs and new coil packs (OEM RSX-spec parts) were installed at same time as the '03 ECM.
- Plugs look okay, maybe a little rich, although their gaps had definitely opened up a bit (around .048, vs. service limit of .051). None were loose.
- It's hard to visually detect any issues with the coil packs, but they "look" normal, even when hot after a drive. (Some of my badly blown/fried coil packs exhibited a bluish "crackle" pattern in the top when hot.)
- Fuel injectors are original, so just 63K miles, but of course (along with the car) they're over 17 years old now...

So, for now, I've done the "MAP whack", and ordered new platinum OE NGK plugs (and re-gapped the current ones to .045 in the meantime). Was thinking of getting the injectors tested and cleaned by a local shop that has a specialized rig for that service.

Any other thoughts on what might be causing it? (Grounding issues? Battery issues?) Really hoping I don't need another ECM.

UPDATE: Turned out to be the MAP sensor! See post below.

 

I had an intermittent misfire that resulted in a slight, random shake at idle, and an occasional puffing out of the exhaust that got worse and worse as the weeks passed -- all with no CEL.

In my experience, you can't visually diagnose a coil pack that is only starting to fail. For me, I bought one new coil pack, and slowly rotated it across cylinders (kept it in a single position per day) until I was able to rule out coil packs entirely; it ended up being my 4th and last coil pack that was starting to fail.

What caused the ECM (ECU?) and coil packs to be fried previously?

 

i think you need MY09 air filter.

 

have you done a valve adjustment? It corrected my misfire.

darcy

 

I'm banking on coil packs.

 

I'm declaring victory with new plugs. Regapping the old ones reduced the issue by 99%, and with new NGKs it's absolutely purring like a kitten. Heck,even the valves seem less noisy.

I think I'd just pushed the old plugs a little too far - combination of a large gap and the plugs being one step colder than stock (24 vs 22).

Thanks everyone!

 

UPDATE: Plugs were not the answer - turns out it was the MAP sensor.

Basically the issue returned - slowly at first, then increasingly worse, until I pulled out one day and it bucked so much I immediately did a U-turn and still almost didn't make it back into the driveway. And yet, still no CEL, and no pending codes! On a hunch, I let the car idle and did another MAP whack, and the motor suddenly surged up and down, and the ECM immediately threw a code (generic TPS code, forget the number). So I ordered a new MAP -- and a set of coil packs, just in case. Sure enough, swapping in the coil packs made no difference, but the new MAP completely transformed the car! It isn't just that the misfire is gone - everything about the motor is smoother and more responsive. Maybe the biggest difference is throttle tip-in, which is now absolutely seamless.

Anyway, just thought I'd share, since even though the "MAP whack" is one of the oldest bits of S2K lore, having one fail completely didn't seem very common. I suspect as these cars continue to age (mine turns 18 in September) we'll see more and more sensor failures.

 

thanks for the update.

part of the MAP sensor TSB was to secure the sensor with a zip tie.

 

Yeah I'd had the TSB done back in the day. Had to clip the original zip tie to change it, but I kept the rest of the little plastic cover piece from the TSB and just wrapped it all with a new zip tie.