Hey,
I have a 2000 Prelude and ever since I bought it in December, I have had issues with a random multiple misfire. The only time I have noticed it misfiring is at idle and its not a common occurrence. It is just every now and then and it seems to only happen when the car is warmed up. I have 7 fault codes. P0301, P0302, P0303, P0304, P0401, P0300, and P1399. P0300-P0304 are all misfire codes and P0401 is for the EGR insufficient flow. P1399 is some Honda specific code that when I look it up on AllData it just says "P1399 is a random misfire code and Honda/Acura has reported for various models that this could be caused by clogged EGR ports. In addition there is the possibility that the valve clearance specification may be out of range." I adjusted my valve clearance and I know that the ports on the intake manifold are clogged with carbon and need to be cleaned out but I would think that it wouldn't cause a misfire at idle if the EGR was restricted because there is no vacuum in the line to it at idle. The EGR usually operates when the car is decelerating and coasting. I haven't gotten the time to clean the ports cause it takes a few hours and I need to get the new caps from Honda as well as get a slide hammer. I have cleaned the valve itself numerous times and at the moment I have a blockoff plate in there with the vacuum line plugged. It still misfires so that leads me to believe that it is something other than the EGR causing the misfire. I have noticed that the short term fuel trim is at -17% while idling sometimes and I was wondering if anybody had any ideas other than clogged injectors. It is weird that it happens in every cylinder but its completely random and usually takes a couple weeks to occur in every cylinder. I replaced the spark plugs because I didn't know how old the ones in it were and the porcelain part of them was a little burnt and light brown colored. The car still had the original timing belt at 119,000 so the previous owner kind of neglected this cars issues. Any help would be greatly appreciated.
Thanks

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nee ! post

Try sea foam treatment.

I already did

Do u have any vac leaks?

So first question..
-How longs it been since the plug wires/cap/rotor were replaced?
-What spark plugs did you use when you replaced them?
-Have you checked you ignition timing?
-You said you already tryed Seafoam, in which way did you use it? Ie; vacuum line, fuel tank or oil?

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Stuck on in Iraq Right now! Aug 09' - ???
Pearl White 98 Prelude Base ~H23A Blue Top! ~
:::Rebel_luder98::: 98 Base
Great Info By 98vtec!!

I replaced the plugs with the NGK Laser Platinums that are the OEM ones(the part number is on a sticker under the hood) The wires look brand new and they have continuity and do not short out to anything. I did not check the ignition timing, thank you that is a good idea and I didn't even think of that. I put the seafoam in the gas tank thinking maybe my fuel rail was a little clogged or something. I have not checked for vacuum leaks.

Ya i'd say double check you ignition timing, might try seafoam through a vacuum line(wouldnt hurt). If everything checks out, I'd have to guess your ignitor is going out.

__________________
Stuck on in Iraq Right now! Aug 09' - ???
Pearl White 98 Prelude Base ~H23A Blue Top! ~
:::Rebel_luder98::: 98 Base
Great Info By 98vtec!!

Thank you, I'll check into that when I get time and let you know if that helped.

Well I got around to cleaning my EGR ports yesterday and I haven't gotten a CEL so I think it's fixed.

It misfired again... in cylinders 1 and 3

This time it wasn't at idle and this is the freeze frame.
Engine Load = 91.765 %
Engine Coolant Temperature = 197.6 °F
Fuel Trim Bank 1 Short Term = 0 %
Fuel Trim Bank 1 Long Term = -0.781 %
Intake Manifold Pressure = 13.489 psi
Engine RPM = 3,904 rpm
Speed (OBD) = 32.311 mph
Intake Air Temperature = 122 °F
Throttle Position(Manifold) = 68.235 %

I had P1399 until I cleaned my EGR. Are you running maybe low octane? I've heard it could cause misfire in some cases

I use 91 octane so it wouldn't be that

I'm having the same issues. Cleaned EGR port's, plugs. Guess i'll try wires and cap next. No problem for me when driving. Only when taken out of gear into N, RPM's drops basically to nothing, stalling sometimes.

Hi, I have a 2000 honda prelude runs fine getting check engine light with codes P0301 P0302 P0303 P1399 P0300 all misfires engine seems fine to me already replaced catalytic convertor's oxygen sensor and installed new ngk iridium lx spark plugs."

Have you removed the cap to inspect the inside of the cap and rotor? Corrosion likes to build up in there. I see where u mentioned plugs and wires, but nothing about cap/rotor

Also not mentioned: make sure your vacuum lines running to/from your EGR Valve and Solenoid are hooked up correctly. When I rebuilt my head, I reversed the lines, and it stumped me for a little while (ran like crap after warmed up).

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2001 Honda Prelude Base

Can you show a picture of the correct order of said vacuum lines, I'm having same issues as mentioned. I did my EGR port plug removal, cleaning and reinstallation. I have new factory Honda EGR Valve and the EGR valve port is clean. Fuel and spark check out, so I'm thinking it's probably vacuum.

Where are the hoses you have doubts where it connects to?

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Resuscitate.

I HAD INSUFFICIENT FLOW EGR Till I switched to 93 octane.

so you good now?

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Resuscitate.