Misfire on First Start-up

I have a '99 C2 with 67k mi. that I've had for about a year. The 60k service was completed by the PO. The past three mornings I've been getting misfires in cylinders 1 and 3 per the codes (P0300, P0301, and P0303). The car will run real rough and if I can nurse it through the misfires it is fine the rest of the day. Smooth through the RPM range and no codes or start issues. I did some searching and ran through the misfire trouble shooting guide. The plugs look perfect, coil resistance within spec, and no damage to the coil body or connectors. They look essentially new. Bad gas or maybe a coolant temp sensor going bad? This is the third little thing to go wrong in the last three weeks. AOS coolant hose leak, bad ignition switch and now misfires. Gotta love old cars.

Sticking cam adjuster causing irratic misfiring maybe.

I thought a misfire related to the adjuster would occur above idle speeds, no?

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Last thing touched...What was done about the AOS hose leak? Any chance someone disturbed the coils/plugs? Did the CEL flash? If it flashed this is signaling a rich misfire which could be leaking injectors. If it doesn't flash, then the misfires are lean in nature and I can't think of a failure mode off hand that would confine itself to affecting just one bank. Bad gas or a bad coolant temp sensor or even a bad MAF are problems common to both banks and thus one could expect (though there are always the exception) misfires from at least one cylinder from the other bank would be present. What's the weather been like the last 3 days there? Has it turned off cool, damp maybe? The times (3) my cars have generated any misfire error codes (with at least one time a rougher than normal engine at cold start) the weather had turned cooler, damper, or in one case I left the car parked outside during a very heavy/prolonged rainstorm. Most recently -- at hotel parking lot in Berkeley this last Wed. night -- the car was outside and a dense marine layer came in. Yet another long shot...but if the 60K service included plugs then the plugs have to be suspect. Maybe not bad plugs, but maybe one or more not torqued properly or someone didn't get the coils connected to its plug ok. Yet another source of misfires is the coil's electrical connector to the wiring harness may not be secure or have some surface corrosion. IOWs, last thing touched -- even if 7K miles back -- is suspect. (On a side note I had the plugs changed in another car and around 3K miles later a misfire developed. I traced this down to one plug wire that had not be properly secured to the plug and to make matters worse the arcing eroded the connector just enough it would not snap tight to the plug. I bought a pair of pliers and squeezed the connector so it would snap onto the plug. This fixed the misfire and as soon as I could I bought a new set of plug wires which I tossed into the trunk yet never had reason to install and included the unopened box of new plug wires with the car when I sold it much later.) Sincerely, Macster.

UThe evenings have been getting cooler which has been a big change from the norm this summer. The AOS hose I changed was the one on the front of the engine between the Alt and the, what is that, the power steering pump? Thinking about it, the coolant that leaked and the bit that came out of the overflow hose after I refilled may have ran across the coils/connectors and started the issues. What has me a stumped is why this only happens in the morning, right at startup. I am getting a flashing CEL during the events and it smelled like gas when I pulled the plugs yesterday. I think I may switch the coils to the 4-6 side and see if the issue moves to the other side.

I got the coils into the bright sun today and noticed cracks leading down to the boots. I'm suspecting that coolant penetrated the cracks and damaged the coils. New ones are on order.

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I think with visible cracks in the coils you've id'd the source of the misfires. You can swap coils around, but I'm not a big fan of this coil testing technique. The less the coil/wiring harness connectors get manipulated the better I like it. I'm always concerned about breaking a wire in the harness or bending a pin or pulling a pin out of a connector. Actually, it makes sense the misfires happen when they do. The engine's shut off hot. It cools down, and as the night progresses the ambient air temp drops, and generally humidity goes up. In your car's case, anti-freeze residue attracts moisture from the air and because more of this is in the cracks it pulls moisture right in where it can do the most harm. There's another thing at play. Any salt in anti-freeze residue -- or any salt and salt is a very common mineral and every exposed surface will have a thin layer of it -- and with moisture this salt will migrate to the cracks. In these cracks as the salt dries it expand and this will slowly widen the crack in which it resides. If this kind of salt weathering can fracture (admittedly over time) granite or other rocks exposed to salt spray and drying on a sea shore it can surely wreck havoc on those puny plastic coil housings. Sincerely, Macster.

I had all six coil packs replaced about 30k to 35k miles ago and when I had the car checked out to see what else I might need pending the clutch, IMSB, AOS and all the while your at it stuff the dealer said I had two cracked coils packs. The car runs flawlessly in all weather though. The service writer said to just replace the the two that are cracked before they cause a problem. The mechanic says to replace all six. Thougths on that?

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It depends. If the 6 coils are relatively new with just one (or maybe 2) bad coil(s) which suggests a bad coil is just bad because its suffering from premature failure then replacing the one (or two) bad coil(s) makes sense. If these bad coils are the ones that are most exposed to the elements (tire splash and even water from rain or car washes) this also makes a case for just replacing them. Absent any misfires from any other cylinders and an inspection of the other coils *not* finding any reasons to replace them then leaving them in service makes sense. (I might add I have gotten darn good life from the coils in my Boxster -- they are original and with over 258K miles on them -- and even in my Turbo -- 96K miles on the original coils, so I lean towards leaving the coils in service until (and so far this has not happened in my case) the coils signal they need to be replaced. It helps though that I live/drive in a region that appears to be quite conducive to prolonged coil life. Otoh, there are I believe areas that are not coil friendly. I read about coil failure at low miles in UK cars and I suspect the weather there accounts for shortened coil life. Same in other regions of the USA.) OTOH, if the coils have a lot of miles on them and coil issues are common where you live/drive -- due to mainly (I suspect) weather conditions -- replacing all 6 'while you are there' makes some sense. Techs differ in their philosophy I guess. Where I take my cars the feedback/advice I get from the techs that work on my cars is if it ain't broke don't fix it. Thus when I have the cars in for plugs while the tech inspected the coils he found no justification to have him replace them, so they were left in service. Since I have so many miles on these coils even if one or more should act up and I have to pay to have the coils replaced in between plug services I'm still money ahead compared to what I would have spent replacing the coils much more frequently with no symptoms even hinting at any coil problems. In short I really don't have an answer. You have to decide what you think is the best course of action for you, your situation, and follow it. Sincerely, Macster.

I replace all six coils, which all had similar cracking leading down to the boots, and no more issues starting the car. Problem solved. Thanks for the input.

Not so fast... The issues have resurfaced and I'm getting misfires on both sides now. I've replaced all six coils, replaced the plugs (which looked good to start with), and made sure that all the coils connected with a nice "click". The codes I'm getting right now are P0102, P1316, P1313, P1319 and P0306. This only happens during cold starts. I only have an OBD-II reader, so my diagnostics are limited to the reader and a multi-meter. I'm thinking I'll have to break down and take it to my independent.

I would stop driving this car until you have the IMS checked and the timing chains looked at

IMS / RMS was replaced in May. The misfires are just associated with startup. Once the car fires and the the ignition events settle, the car runs perfect and smooth through the rev range. I wouldn't expect this to be the case if there were issues with cam timing.

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I think that P0102 is the key: Bad MAF. I know of one case where misfires were traced to a bad MAF. But I wouldn't replace it on just that P0102 error and my opinion alone. Disconnect the MAF at the wiring harness. Clear codes even though there may not be any active codes. This resets all trims/etc to their defaults. Drive the car. No need to get all crazy. Just drive the car normally. What the car/engine does or doesn't do determines what you do next. If the symptoms remain.. nevermind. (Well, come back and we'll talk.) If the symptoms do not remain, reconnect the MAF, clear the codes again and drive the car so more and see if the symptoms return. It is my layman's opinion there's nothing scary going on (though wait until you price a new MAF) but always if symptoms get worse, if the engine starts making sounds, etc., shut off the engine pronto and do not run it again until you have the car at a qualified shop with a professional/qualified Porsche tech at your side to advise you. Sincerely, Macster.

Im not trying to be doom and gloom.. but what about antifreeze in the cylinders? does it smell at all when you crank it up?

Sharky - My coolant levels have remained constant, and I've noticed no coolant smell or white smoke at startup. I'm due for an oil change in 1k and I don't expect to see any intermix issues. So, I cleaned the MAF as a preventative measure, changed the plugs and re-checked my coil connectors. The last 3 days there have been no misfire issues and no codes. Car has run smooth and powerful. Cross your fingers, but I think it's solved.

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Taking the car to your indy shop is not a bad idea. The errors are misfires, emissions related, which I take to mean are rich misfires. The risk from rich misfires is this dumps raw gas into the converters which can damage the converters. You do not want to damage them for they are expensive (>$1K/each parts cost alone) to replace. If you insist on going ahead with self-diagnosis and realize there is a risk to the converters, and maybe the engine too, one thing you can try with your reader -- provided it supports OBD data viewing -- is to look at intake air temperature, coolant temperature at/shortly after cold engine start to see if either of these differ too much from each other or from what the ambient temperature is. If you see a difference of opinion between the intake air temp and what you know ambient temp is you can suspect the MAF, which is also responsible for the intake air temp. The same applies to the coolant temperature sensor reading and ambient. But I mentioned intake air temp first, because the P0102 is a MAF below limit which points to a MAF problem. P0102 can arise from an open circuit, short circuit to ground, MAF faulty. The wiring from the MAF to the DME must be checked for continuity, the wiring from the MAF to the DME must be checked for a short to ground, the signal from the MAF must be checked, and last but not least the engine air filter air box cleaned and the the filter element replaced. The 1st 3 require some "special" tools and a good knowledge of these cars their wiring systems. The DME can be severely damaged -- read ruined -- if one is trying to test for continuity or a short in the wiring and he static discharges into the wiring that leads to the DME. Sincerely, Macster.