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troubleshoot flashing CEL, P0300 P0301 Low RPM misfire, 2000 Boxster S


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My 2000 Boxster S w/105k (body) 40k (engine) is acting up.

Last fall, I got caught in downpour and inches of standing water, getting splashed hard by other cars. The CEL started flashing and the car was nearly impossible to drive past 3rd gear (no power and bucking) until I could get off freeway to let it dry out. It had several misfire codes set.

Ever since then, it's been a little less smooth than I had been accustomed to, and now it is misfiring and bucking below about 2600 RPM all gears, all temps, but ONLY with high throttle opening (e-gas). Tipping the throttle in seems to be fine. High RPM seems ok, if maybe a little weak. If you keep the throttle open under the misifiring conditions, it will cause a flashing CEL, although it will not stay on. Stored codes are P0300, P0301.

Previously, the secondary air injector and catalyst codes have set the CEL, but it went away on their own (this was after driving on a very dusty road last fall).

Car is stock, except desnorkel. Half of exhaust was disconnected recently for wheel bearing replacement, but this problem predates that job.

Have changed plugs, cleaned MAF, cleaned throttle body. Most of the coils are cracked, but not bad enough to see inside -- I epoxied them. Problem seemed to clear up after changing plugs, but then came back on next drive.

I suspect bad coil(s), also MAF or vacuum leaks.

My understanding is that the coils should have about 40k miles on them (same as engine), but they do look pretty rough.

I am ordering coils, but want to make this problem go away permanently without playing the blind remove and replace game -- what else should I look at? I will disconnect the MAF and drive around to see if that helps and do a propane vacuum leak check as well when the engine lid is off.

Thanks so much guys,

Cary

(photo is from Utah, 3k into my 10k mile summer roadtrip last year, car was awesome!)

post-69049-0-55806600-1333042055_thumb.j

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  • Moderators

I'm afraid you went in the wrong direction when you tried to epoxy cracked coil packs, which simply ain't gonna work. They will open up again.

Pull the coil packs; replace any they look even remotely bad; if they are all original to the car, you may want to just do them all.

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Two approaches: 1) Use a smoke gun; or 2) Use a butane or propane source on slow bleed around the suspected areas. Note of caution: Obviously propane or butane are highly flamable, do it outside on a relatively calm day and you should be fine. And NO SMOKING........

Smoke will get sucked into the leaks with the car at idle, showing you where they are visually; propane or butane will cause a sudden jump in RPM's for the same reason..............

What gives you the impression that you have a vacuum leak?

Next time you need Porsche OEM parts, give board sponsor Sunset Porsche a call (toll free), they will probably surprise you with their pricing...........

Edited by JFP in PA
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Nothing is particularly pointing towards vacuum leaks, but I'd like to eliminate that as a cause if the coil packs don't fix it.

Reason I asked is that vacuum leaks almost inevitably cause specific codes to appear, which you have not mentioned. You should also note that your MAF had almost no impact on the car's idle conditions. Do the coils and let us know how it panned out.....

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Not recommended to operate the vehicle if the engine is misfiring and the check engine light is flashing, you risk damage to the catalytic convertors. I would replace all the ignition coils and carefully inspect the coil electrical connectors for corrosion as yo mentioned driving through excessive amounts of water.

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Replaced coil #1, and now it runs like a Porsche again! Pulls smoothly with more power than I've had since roughness began. I can pull away in 2nd again, whereas before I couldn't shift until 15 without bucking.

Thanks for the input guys.

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Replaced coil #1, and now it runs like a Porsche again! Pulls smoothly with more power than I've had since roughness began. I can pull away in 2nd again, whereas before I couldn't shift until 15 without bucking.

Thanks for the input guys.

Thought so; glad to be of help..............

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