CEL Flashing, Shaky Engine and Misfires
 

Hi all! I believe I have come across a rather serious issue with my 2004 986 S (3.2). I went to turn it on today and it struggled a little but turned on, I was greeted with quite a rough shake while idle then I decided to drive a little bit (not even 300m) when it started to misfire. So I immediately turned around and turned the car off completely.

What could have caused this issue and is it as serious as I believe to be?

Thanks in advance!

Do you have a code reader? Codes will help pinpoint the problem.

Did you or someone recently do engine work on your car?

Help us help you.

It did have a major service in June at my local Porsche garage and was running perfectly up until now. Unfortunately I don't have a code reader😔

A lot can happen to a Boxster in the 6 months since your major service.

You can obtain a generic code reader from several online sources. If you have a Harbor Freight near you, they sell OBD II readers at a reasonable price. A Porsche-specific tool such as a Durametric is a better option, but it is more expensive. If you plan to DIY often on your Boxster and keep it for several years, a Durametric is a worthwhile investment.

If you don't know the codes, you will be guessing at the cause of the problem. For example, you could have a misfire on one of your cylinders. A code reader will tell you which cylinder is misfiring. You could then perform some simple tests to identify the solution. If it is a cylinder misfire, some potential causes are (1) A damaged coil pack; (2) A damaged spark plug; (3) Poor compression on the cylinder; or (4) A damaged fuel injector.

Taking this example further, say that the code reader identifies a misfire on cylinder 3, you can swap the coil pack from an adjacent cylinder and determine whether the misfire moves to the other cylinder. That would tell you the problem was likely a defective coil pack. If the misfire doesn't "move" you might have one of the other problems.

Please keep in mind that your problem could be elsewhere such as with the Mass Air Flow Sensor. Having the code will point you in the right direction.

Also, don't drive the car for a prolonged period with a flashing CEL. The engine will be passing unburned gasoline into the catalytic converter which is very hot when it is at operating temperature. You don't want to risk a fire.

Good luck.

Thank you for such a detailed response. I'm gonna contact Porsche soon to see if I can get an appointment to have it towed there. I'm not risking turning the engine on again until it's safe.

I think that is a good decision. I see that you are located in Spain and appreciate that you may not have a typical U.S. suburban garage in which you can DIY repairs. In the U.S. auto parts stores will normally read OBD II codes for you, but I don't know whether that is the case in Spain.

If you are interested in the process for diagnosing the flashing Check Engine Light, this video provides a decent outline.

https://www.youtube.com/watch?v=PK8pca8q5Zo

In the video, the presenter decided the spark plugs were defective. In my experience, I've found that spark plugs are a less likely source of the problem. Of the three flashing Check Engine Lights I've experienced, two were caused by defective coils and one was caused by a defective Mass Air Flow sensor. Based on this, I think it is likely you have a defective coil pack, but that is just a hunch. Replacing a coil on a Boxster requires jacking up the car, placing it on jack stands and removing the rear fender liner. It is not terribly difficult, but you need a safe place to work and appropriate tools. This video shows the process:

https://www.youtube.com/watch?v=H25qLssQNxg