Yesterday I took my 991.1 out because it was a nice day and around midday (after driving the car for 15+ miles), I got into my car to leave an appointment and the car died at a stop light. I restarted it and it was idling very lumpy and the "fault engine control, possible to drive on" yellow warning light came on. I limped it home (it felt like it was running on 3-4 cylinders) and used my friend's OBD2 to see what codes were thrown.

It came back with the following codes:

- 0300 (random misfire detected)
- 0304 (cylinder 4 misfire detected)
- 0305 (cylinder 5 misfire detected)
- 0306 (cylinder 6 misfire detected)

I reset the codes and took it out and it ran normally yesterday evening. This morning I drove it again and it drove normally. But then around 11:00 am I started it and it was idling rough again. I shut it down and waited a few minutes and started it again, and it was fine. I just drove it home and put it in the garage.

My warranty just expired (of course), and my nearest Porsche dealership is 120 miles away. Porsche pulled my local dealership a few years ago, and one of the Porsche techs who worked there now works at a local import service shop, but he has limited experience with 991s. They also charge nearly as much per hour ($120) as the dealerships.

Looking for some advice. I have next to zero technical knowledge of cars, so I'm kinda flying blind here. From my limited research, I'm finding since its an entire bank of cylinders, it could be the coils or possibly plug wires?

 

Probably one coil per plug - sounds like a fuel rail or something to me, maybe a clogged filter.

 

Each spark plug has its own ignition coil, so I would doubt that it's coil-related for three to go out at once.

EDIT: Cylinders 4, 5 and 6 are on the passenger side of the car.

 

Had a similar situation w/cylinders 5&6 without the stumble. Dealer stated both cylinders misfired, but cleared itself. Happened again a week later, but again cleared itself. A year later, same thing. (3000 miles). Dealer was told to reprogram all the computers by Germany. Had the car 9 days but resolved the problem.

 

Pretty safe to rule out ignition coils or spark plugs since three cylinders misfired. Sounds like a sensor or corrupt ECU. How many miles on the engine? PDK or Manual? Was the engine overre'd recently (last few months)?

 

PDK, 13,000 miles, not overrevved recently.

 

Do let us know when this has been straightened out. Doubtful that its anything serious given the mileage, no recent over rev's and engine series. Now, if this was 2014 GT3 that would be a different story!

 

Have you checked your 02 sensors. Sounds to me like a sensor or loose wire.

ChuckJ

 

I spoke to a service advisor at my nearest Porsche dealer today and gave him all of the information I had. He said the first thing they would do is change the plugs and ignition coils. So I ordered plugs and ignition coils from Suncoast today, and I'm going to have a local shop perform the labor.

Is this a difficult task, or should installing plugs and coils be pretty straightforward for a mechanic who doesn't work on very many 991s?

 

Simple and straightforward

 

Be sure that the technician has a 12 point 14mm deep spark plug socket with a magnetic insert to keep the plug in the socket when removing and installing. Torque the plugs between 14-19 lbs. Heat shield on each side have to be first be removed. No need to remove wheels but it does make the forward plugs more accessible.

 

Think ur barking up the wrong tree. As I said before, took a total reload of the software to resolve the same issue. Have ur dealer look it up on the Porsche factory forum. Leith Porsche.

Good luck.

 

I tend to agree, but the car is 4 years old, so nothing wrong with changing the plugs and coils as a first step to rule out the obvious.

Since my warranty has expired, anyone have an idea what a total reload of the software would cost? This ordeal is making me nervous.

 

Replaced spark plugs and ignition coils today, and just as most of us figured, it didn't resolve the problem. Still misfiring on cylinders 4, 5 and 6. Indy tech thinks we should start replacing O2 sensors. Called to order 02 sensors and I'm speaking to the rep, told him my issue, and he insists that will not resolve my problem. Suggests it could be camshaft sensor. I'm thinking maybe the high pressure fuel pump?

Who knows . . . I'm getting frustrated. I'm almost to the point of sucking it up and having it towed 130 miles to nearest Porsche dealer.