I had this error P0300 with P0301 &P0302 on my 2002 Honda S2000 at 104k miles, first fault I have had since buying the car at 36K miles.
Exec Summary: fault was Injectors 1&2 flow rates down buy 7%
Solution Ultrasonic cleaning of all injectors.
I read lots of threads about people with this problem and not many threads documented the solution. So this is my first thread letting you know how I solved it, to save you reading as many dead end threads as I did.
Remember this fault could be caused by many things so I am only explaining the solution to the problem I had; but the sequence I describe may help you find yours at the lowest cost.
Firstly you must have a DCT error code reader, without one don't bother doing it yourself. You will need an OBDII reader which allows you to clear codes & view pending codes aswell as saved codes. I used either proscan or scanXL with an ELM327 interface.
The error P1399 is a pending missfire code. Which registers the first time the ECU sees a missfire. It holds this code until the following driving cycle. (eg ignition off and the immobiliser enabled). Then when it sees the missfire the next time the engine is running, it will report the P0300 code along with which cylinders it sees the missfire on and illuminates the MIL light on the dash. A missfire is registered when the cranksharft rpm sensor varies by more than 2% across the firing order.. 1-3-4-2
Something to note with this problem which I read in another thread and seemed true in my investigations was that the first code to appear seems to be the one/ones to focus on. I would always have P0301 or P0302 sometimes followed by P0304 if I ran the engine long enough. But my problem was really only with cylinders 1 & 2.
If you can, extract the freeze frame data for the error code. My fault was happening at low rpm or idle. infact once the MIL light came on I did notice the engine running slightly unevenly at idle. It also had a +10% short term fuel trim which means it was adding more fuel than expected to maintain the specific O2 emissions.
Check the valve clearances. costs no money and you should eliminate this as a possbile problem.
I only had to adjust a couple slighty and did not solve the problem
Check for a Coil pack fault & Spark plugs. move the coil pack from the missfiring cylinder to a cylinder as much out of phase in the the firing order as possible. eg firing order is 1-3-4-2 and if the error is on cyl 1 (P0301) then move it to cyl 4. If you see the error code change from P0301 to P0304 then the coil pack could be your problem... clear and repeat the test several times also return the coil to its original position and make sure the error moves back to make sure as the coil packs are around £130.
Also carry out the same as above but with the spark plugs moving and leaving the coil packs in the same position.
I did not find a fault with the coils or the plugs.
My plugs had never been changed since new and the service manual recommends changing them at 100K miles so I did this anyway. The Genuine honda plugs cost me around £60.
Car now runs a lot smoother across all the rpm range. but I still had the missfire code.
Compression test: you need a compression tester for this.. around £20. all sparks plugs out, the throttle open with the engine cold. Mine read 220,220,225,220PSI which is within the spec for variation of 28PSI. I have seen results as low as 190PSI and as high as 240PSI on other threads
If you see a problem then you will need to do a leak down test to check for damaged piston rings or poorly seated valves.
but this looked ok for me no major variation.
Clean the air intake system. This will cost the price of the throttle body gasket and an (Idle Air Control Valve) IACV seal. Roughly £10.
The oil return system from the crank case adds a lot of oil to the intake area of the manifold. So a clean is a good thing to do anyway. avoid the MAP Thwack, if you have a screw driver in your hand, unscrew the MAP sensor and clean it properly, remove the throttle body and IACV and clean out all the oil residue in the channels that you can. The valve on the IACV is sprung loaded so a clean of this helps its operation.
There was a definate improvement in the acceleration from idle but it did not solve the Missfire Code from coming up.
Fuel adatives to clean the injectors. Cost around £20. 99% chance this will not solve your problem. But with the focus now being on the injectors being dirty or blocked its worth cleaning out the system an pipes get as much dirt up to the injectors so that if you do clean the injectors they won't just get blocked again by the next loose bit of dirt in the pipe.
The S2000 fuel filter is not the best and having used predominantly cheap tesco fuel I found using the additive made the error more frequent.. but did the job of clearing the dirt in the system.
Test fuel injectors. This is more advanced and will require some ability to perform.. do not try this unless you are confident and follow the workshop manual instructions. A 22mm torque spanner (not socket wrench) will be required for this. They cost around £30. Also buy new injector seals top & bottom and Fuel banjo washers approx £20 for all. Cost to ultrasonicly clean all the injectors £70.
Once you have removed all the injectors and cleaned the exteria and around the manifold openings to ensure that there are no air leaks. Re assemble with the injectors in a different order as with the coil packs.. eg firing order is 1-3-4-2 and if the error is on cyl 1 (P0301) then move it to cyl 4
I swapped 1&2 with 3&4. after doing this I notice that the error codes changed from P0301 &P0302 appearing first to P0304 & P0303 appearing first.
So I looked for a garage which had ANSU injector cleaning machine.. check thier web site as they have a list of garages who have one.
The injectors looked to be spraying evenly but when conducting the flow test the injectors 1 & 2's flow rates were 7% down on 3 & 4's. This is not a lot but after cleaning it was reduced to 4%
Re-assembly the injectors back into the car. I found the error was fixed. Idle is now very smooth better than when I purchased it at 36K miles. Also I noticed all the little rattles in the cabin at idle seem to have stopped. Also my fuel consuption is up by 5-10% use to get 250miles to the tank now around 270miles to the tank.
I expect that I will need to clean the injectors again at some point if the error reappears. But its cheaper than a new pair at £250 each.
So far 2000 miles with no error codes or pending codes.
Hope this helped