Hey guys, I have a Honda S2000 2005, only mod done to it is a K&n fuel air intake.
codes: PO300, PO301, PO302, PO303, PO304
The misfires start after the car is warmed up, but when I drive the car I'm pretty sure there is no misfire, only at idle (the rpm doesn't jump around at idle)
a few weeks ago I had misfires in all four cylinders,
I did a compression test
Spark plugs were changed less then 2k miles ago.
I did a valve lash
checked fuel pressure
I can hear the misfires so I know I have them
still have all four cylinder misfires.
(I didn't change out the coils, or injectors, and I know those could be a possible fix, but read on)
a week later
I check the codes again, and now I only have misfire in cylinder one, I don't think S2000's are that amazing that they can just fix themselves like that
Only code now is PO301
Problem 2
I had a code 23
"engine speed signal circuit low or high"
When I brake my wheel sometimes pushes to the left instead of staying straight (it isn't tire pressure)

Anyone know any of the possible fixes?

 

Did you alter any of the intake sensors or connections when you put the K&N air filter onto the car?


"I had a code 23."

P023 or P0123?

P0123 is a throttle position sensor issue.

 

Try a new ecu, had the same problem on my 00 got a 02 ecu and it finally fixed it, I tried everything to fix it.

 

I would suggest this as a last resort. Definitely exhaust the options in the Misfire thread first.

 

I've seen alternators on these cars cause misfires. Are you gauges flickering even in the slightest bit?

 

What were your compression readings?

 

All of them are at 240 and Last cylinder is 250

 

This might sound weird but did you recently run out of gas, do any type of hard driving or hit some off road patches, blown motor mounts, or do/have any serious work done to the engine that involved touching the crank position sensor?

Only reason I ask is because when people run out of gas, the vehicle chokes up and we'd get that engine speed fault code because the crank position sensor jumps and can't see a tooth for a split second so it thinks the crank position sensor is bad. I'd first check to see if that sensor is bolted down.

Next up is to do a real fuel pressure test. To be up front, I'm more of a Mercedes expert than I am a S2K expert (I work for Benz) and we have fuel pressure sensors in our more recent vehicle's so I'm not sure if S2K's have anything that monitor fuel pressure that would throw a code. But if there isn't (maybe a more senior S2K owner can chime in here) there is a high chance that is the source of your problem.

If that also passes, check continuity in your crank position sensor. That sensor should be using a 5 volt reference (again, might need a more senior owner to chime in) if it's not receiving proper voltage you may have unnecessary resistance in that sensor/wiring causing inconsistent read, thus misfires. That's only if you have a DMM. If not then just buy a crank position sensor, they can't be more than 50 bucks.

Another thing to look at is O2 sensor. From your story this doesn't happen when the engine is cold but only when hot and at idle. Basically when the O2 sensor is ignored, you have no misfire, when your engine starts receiving input from O2 sensor, it starts misfiring. If you scanned your vehicle again with a better scanner and grabbed snapshots of when the misfire occured and how many occurances, that'll give you (and us) a better understanding of what is going on. This is a tricky code because you can misfire because of the crank position sensor or the misfire could cause the engine speed signal fault. Things like throttle %, ambient temp., and engine speed are all things that play a huge role in the misfire.

If you don't have a scan tool that can read that then can you tell us when it gets worse? Information that would be super helpful would be; morning, night, cold day, hot day, humid day, dry day, after a drive, before a drive, after cruising and coming to a complete stop, when accelerating does the car bog, what do you fill up with, where do you live, what happened and what were you doing when the check engine light first turned on, and what were you doing before the check engine light came on?

Sorry ahead of time if some of this doesn't apply to the S2K, I'm no S2K expert but I'm no stranger to diag from dealership experience.