I could really use some help here. My 2001 S2000 has a random misfire at idle. The first code is always 1399, but after a short time I'll have codes for a couple cylinders. Cylinder three (p0303) is consistently the first cylinder to code, but the rest follow until I pull 1399, 0300, 0301, 0302, 0303, 0304.

The misfire happens ONLY at idle, and I get a flashing CEL. Reving the car or pulling away from the light instantly makes the CEL go solid again. The car feels and drives just fine during the entire RPM range, goes into VTEC just fine, however it idles rough.

Here is what I've done so far:

- Replaced MAP with brand new OEM unit
- Switch Coil #3 and #2 (cylinder 2 is often the last to code a misfire) - No change, misfire still started in #3 and #2 is often the last to code
- Ultrasonically cleaned all 4 injectors - car felt slightly smoother, but no change in misfire idle issue.
- Replaced injectors
- Two valve adjustment's
- Cleaned ISV - car felt better, but no change in Misfire issue
- Replaced spark plugs
- Replaced PCV valve
- Replaced timing chain tensioner

I haven't ever mis-shifted or over-reved the car, so I don't expect the issue to be bent valves.

I've read tons of threads on here, most of the suggestions haven't worked or don't seem like my situation.

Anyone have any suggestions on what my next few steps should be, or have had the same issue with a fix?

Thanks so much for the help!

 

Did this just start to happen all the sudden?

Did you recently fill up with fuel?

How many miles are on the engine?

 

Been going on for a few months now, been through many many tanks of gas.

The engine has over 100K on it.

 

Can you take a peek at the back of the intake valves to see if they have excessive amounts of carbon?

How old is the fuel filter?

How did the old plugs look? white/grey/black?

Do you know anyone with a scan tool/diagnostic computer to monitor sensor values while driving?

 

do a leakdown test. If you've done all of the above, I think its time to do a leakdown. Sometimes if your gasket could be compromised, I've noticed, rough idle and just a slight bobble when I crack the throttle. Ran fine I thought everywhere else, then did a leakdown and found my gasket was leaking between cylinders. Do a leakdown and not a misleading compression test.

 

When I replaced the injectors, I checked the back of the valves. There was some carbon on there, but nothing excessive.

I haven't replaced the fuel filter, so I assume it's original.

IIRC, the plugs were black, except for the tips which were Grey.

I don't have access to anything beyond a standard code puller. I've been in contact with the guys at http://apexspeedtech.com/ and plan to take it there if I cannot resolve this on my own.

You didn't experience any additional pressure in the cooling system, running hot, or oil in the coolant? I've checked for these and all seems normal.

 

Ive had something similar happen to me. No coolant loss, no intermixing, no overheating. A leakdown test showed leakage between cylinders 2 and 3. The engine ran surprisingly well considering I had a blown HG...

Might wanna change the fuel filter just for ***** and giggles..

 

It's at the dealer today for a leakdown, test fuel pressure etc. Leakdown tester is 70+ and this was 115, so it was worth it even though I hate taking the car to others...

Will update when I hear back.

 

Alright, got the car back. It's a bent valve in Cylinder #3.

I may just swap so if you've got a swap in socal for a good price, let me know!