Fishah

Hey guys! I did search a bit here but I'm feeling slightly lost. Any thoughts would be appreciated.

Took the car for a spirited drive and filled it up with gas about four days ago. Parked it in the garage; no issues.

Started it up yesterday, backed it out of the garage, and let it idle for a minute while I ran inside to grab something. When I came back, the CEL was on solid.

Code says random misfire cylinder 1 and 5.

I drove the car around and it didn't clear but no symptoms. I cleared the codes and drove for another hour and it didn't come back.

Car is a 2004 AE with 111k miles.

Any idea what could cause two cylinders to misfire randomly after being cold? I could not reproduce it on a hot engine.

Plus are reasonably new from the previous owner. I did do a fuel treatment that I bought from LN when I changed the oil about 500 miles ago.

Thanks everyone!!

P9C

Was that a one time incident or is it misfiring during every cold start?
ps. In this case 1 and 5 and relevant because they are consecutive cylinders in firing order so they are not necessarily just random so it's probable - although not absolutely - that something happened just before or during that time when 5 and then 1 was firing.

jdbornem

You say plugs are newish, but what about coils? They crack and can be a primary cause of random misfires.

dporto

If it’s misfire codes the first thing I’d recommend is coils. I chased a whole bunch of other stuff because my coils only had about 15k mi. on them... big mistake - wasted lots of time (almost all summer last year) and a fair amount of $$ (thank god I did the work myself)... Do yourself a favor and change them out!

P9C

Since it's a cold engine misfiring how'bout intake manifold leak or maybe a minor vacuum leak?

dporto

Could be - mine didn’t misfire til hot...Vacuum leaks shouldn’t be too difficult to track down. You can first try with ether/starting fluid - let car idle and spray around suspected areas of leak, if rpms increase you’ve found your leak. If it’s deeper toward the front of the engine you may have to smoke test...

Fishah

Thanks for the replies everyone!

It did not happen the following day when I did a cold start. So far just a one time incident.

What type of event could cause what you're describing? Something fuel related? A voltage drop? The A/C was running if that makes a different.

Just checked my records. Plugs and Coils are less than 2k miles old.

P.O used a Beru kit: https://www.fcpeuro.com/products/por...ru-996ignclkt1

Do we have any experience with Beru coils? Just wondering what the odds that two new coils on the same bank randomly misfired in succession.

Would there be any other symptoms associated with this?

I wish I was as confident as @dporto lol

dporto

Beru are standard OEM replacement coils. It’s certainly possible that two out of six are defective - but unlikely... I’d start with the vacuum leak route

Fishah

Ok, fun. Thanks! I appreciate your input.

dporto

Come to think of it though... If it idles without stumbling, the chances of a vacuum leak are slim to none...

Imo000

Don't start throwing parts at it hoping it will fix it.

jdbornem

If it doesn't repeat, other than the smoke test, it will be hard to diagnose, and personally I would have a hard time digging into swapping coils until it repeats.
But here goes my thoughts:
If you can, you can do a smoke test for intake/vacuum leaks.
It's a bit of a pain, but you could also swap 1,5 coils with others (marking the suspect ones), and drive for a while to see if the problem repeats and follows them.
I might pull and double check that the plugs look okay while you're there. Coil 5 will be the harder of the two, and so in for a penny in for a pound.

Also, check the engine ground point! There is only one behind the rear passenger wheel just above the coil heat shield. It's easy to access, and could be worth removing, cleaning the contact points, and reinstalling. Many people have chased intermittent coil issues for a long time, only to discover a bad engine ground.

Next would be a fuel issue I think. Others would have to weigh in on trouble troubleshooting that.

Idaho911

I feel attacked.

Hal

I bought a 997 from a good friend. He had had it serviced at a very experienced shop with the owner having been of the crew for a factory 962. That shop put new plugs in the car and told my friend he would never have to change them.

A few years later in my ownership, your CEL’s started popping up. First thought was coil packs. Replaced them. CEL’s came back. Finally pulled the non-standard plugs and replaced with Porsche approved plugs. CEL’s went away and never returned.

YMMV

Fishah

Thanks again guys. The issue did happen again tonight. I heard it stumble once, just briefly, then recovered. Again it was a totally cold engine, idling for about 30 seconds after start when it happened. Again gas tank completely full. Once it stumbles it recovers and idles fine.

Codes say Cyl 1 & 5 again.

I'll definitely check the ground and swapping coils seems like the next best idea.

Could this be related to outside temperature? I live in the desert but both times this happened it was cooler weather than we've been having all summer.

Like, could a battery weakened by the cold cause this?

-

I'll be honest chasing vacuum leaks sounds scary to me.