got a check engine light yesterday and car started running really rough, was misfiring and down on power. my OBII reader gave the following codes; P0300, 301, 302, 303, 304 & 305. which all seam to be cylinder related.

anyone got any ideas where to start to remedy the issue? car seams to be running fine now since turning the engine off and on.

 

Those are misfires, the units digit being the cylinder number that was misfiring. (P0300 signals a general misfire of one or more cylinders.)

Generally misfires are caused by coils that are past their change by date. The lifetime of coils is partially (and primarily I'd dare to say) dependent up climatic conditions where you live and drive.

For instance, I read about coil issues with UK Boxsters about the same age as my car long before reading about coil issues here in the USA with Boxsters about the same age as my car. Since my Boxster has spent the bulk of its time in rather dry climate this helps explain why with nearly 282K miles on the original coils they are still ok.

Plugs can also come in for some suspicion but plugs have to be pretty bad to cause misfires is my experience with other engines.

Barring someone being at the engine recently with the misfires appearing after this I'd hazard a guess the coils are needing to be replaced.

Did you wash the car or did the car sit out in the rain before the misfires? My Turbo has misfired after sitting out all night in a heavy rain storm and once after being out all night in a bad fog. More recently though it has misfired after just being left out in a covered carport with some unusual for this area high humidity.

In the case of the misfires after the rain or fog I just read the codes, cleared them, then drove the car. Since the misfires didn't come back and just as important the engine didn't exhibit any untoward behavior t didn't worry about them.

These latest misfires have me thinking that maybe it is time to replace the coils. Might point out the Turbo has spent its entire life in dry climate but the engine compartment is more exposed to the elements and since it is a Turbo the coils get subjected to the heat from the massive and very hot exhaust system.

My point is if the misfires appeared with no washing or rain or no real damp/humid weather this strongly points to it is time to replace the coils and you might as well change the plugs too.

 

If it's coils, why would the fault disappear after turning the engine off. Ran the car all weekend and it's running great now. Would have thought the coils being damaged would be a permanent misfire?