Julien_Co

Hello everyone,
I am chasing misfire (pending codes) on my 997 C2 (110,000km).
Only on cold start (car not driven for a few days), pending codes for misfire (P0300, P0301, P0302 & P0306). If I cut the engine when it is warm and start it again after 2 minutes (still warm), the pending codes disappear. No Cel. The Cel only appear when I drive the car (which has sat for a few days) only once and don't start it again for a few days. 3 cycles like this and the Cel usually appear (but not flashing). The car runs fine, nothing wrong.
I have changed coils, spark plugs, made vaccum leaks tests, injectors cleaned (by pression not removed).
What could be next? Variocam solenoid bracket?
Thanks a lot in advance!

Macster

Been dealing with what I call cold misfires with my 996 Turbo now for a while. Always DTCs P0303, P0306 and P0300. The engine never misfires at any other times. Never any pending codes either. So I don't suspect any VarioCam Plus issues.

At 132K miles I had new O2 sensors installed -- triggered by an O2 sensor error. Then later at 140K miles I had new coils and plugs installed (coils original), but the same cylinders misfire every time.

On my tech's recommendation I tried a bottle of Swepco fuel system cleaner. Didn't help. I then tried 2 bottles -- one at a time -- of Techron. Didn't help. This is even though I switched to using Chevron gasoline vs. Shell some months prior to trying the fuel system cleaner/Techron.

Car due to go in for its 150K mile service soon. I only have to drive the car another 1200 miles. When I have the car in I'll talk this over with the tech so see if he has any other ideas.

In the meantime to avoid the CEL coming on and having to go through the hassle of pluggin in my OBD2 code reader and reading/writing down the codes and clearing them my work-around is to avoid letting the engine idle any after a cold start. Just a moment or two after cold start I'm backing the car up and heading for the exit driveway. Once on the road -- surface streets -- of course I'm easy on the gas until the engine is fully warmed up. Same as before. Now I just avoid the idle until the idle speed drops which used to take maybe a minute at the most.

dbv1

Do you have those BMC or K&N oiled filters? Those can foul the MAF. Try cleaning the MAF with CRC MAF cleaner, it's quick and easy.

Julien_Co

Thank you for your responses. No K&N air filter and already cleaned the MAF. Could it be the MAF sensor or temp sensor? No risk of damage? If Variocam solenoid bracket is broken, it would affect the entire bank (1,2,3 or 4,5,6 cyl)?

Bruce In Philly

You really need to just read the codes. Go to an Autozone or whatever and they will read them for free.

Peace
Bruce in Philly

Macster

MAF is a possibility. However, misfires are not a common symptom of a bad MAF. In fact I only know of one case of a bad MAF causing misfires and the misfires were limited to one bank. And this was in a Boxster I can't recall the year.

A MAF is a pretty expensive item to just replace without more evidence though.

With an OBD2 code reader/data viewer you can view the MAF output and the air and coolant temperature sensor values in "real time". If you know when the msifires occur you can be viewing this data to see if you can spot something out of the ordinary. 'course, you view this data at other times to so you know what ordinary looks like.

Even better if you can capture/log the data over time. My years old Actron OBD2 code reader/data viewer/data logger only logs about 1 minute's worth of engine telemetry. Newer units though can log for longer and you can download the data to a PC to view. I have no recommendations though as I have not researched these units in some time.

As for damage if the CEL is not flashing and the engine is not manifesting any untoward behavior the odds are there is no risk but 1) I'm not a professional tech; and 2) See (1).

My memory is a Variocam Plus solenoid bracket is not a common failure on these engines. 'course, that doesn't mean it can't occur. So you or a tech needs to check this bracket to make sure it is intact.

Consult with a trusted tech. (I did.) Maybe he'll recommend you try a fuel system cleaner. My tech gave me a bottle of Swepco to use and then when that didn't help I used 2 bottles of Techron, one right after the other, each blended with a full tank of fuel. The bottle actually treats 20 gallons of gasoline but I used the whole bottle in 16+ gallons my Turbo tank holds.

In my case the Techron didn't help.

I used the Techron just 500+ miles before my car was due for its 5K mile oil/filter service. Years ago I was told to change the oil/filter after using Techron and I repeat this that after using Techron it is advisable to change the oil/filter as Techron can add to the engine oil's contamination and you don't want the oil any more contaminated than it gets under normal circumstances.

Julien_Co

Thank you again & again for all your feedback.

dbv1

All the misfires I've seen were either coils or spark plugs. My MAF suggestion is what I heard from other people as cause of their misfires. If you cleaned it, I wouldn't change it just yet. Do you have buddy with the same car? You could swap them. Another thing I've heard that could cause misfires are intake leaks but you've checked that. Oxygen and temperature sensors are another thing that can cause misfires. Good luck.