Bprince_92

Hoping for some help if possible guys. I have a 2007 Boxster S and I am getting cold start misfires on cylinders 1,2 and 3 (all on 1 bank).
When I cold start the car as the revs drop from about 1600rpm the car starts to feel a little rough and the check engine light comes on. The codes are always p0300, p0301, p0302 and p0303, then as the car returns to idle it smooths out again and the CEL turns off. During the day the car runs great and when I show it to the shop they can't detect a misfire but they can see the stored codes.
I have noticed that if I rev the engine and keep the revs up during the cold start I don't seem to get the misfires or the CEL.
I have new spark plugs and new coils. Prior to the coils I had some trouble with starting the car when warm where the car would shake before starting or even stall, but this seems to have improved. However last night I did feel the car shake a little before starting.
Other things to note I do feel as though the car hesitates a little at times when driving, and also my idle is at around 600rpm but I have noticed that between 800 and 1000rpm the car is a little rough. The rest of the RPM range is very smooth.

Any ideas on what may be going on? The shop seems to be a bit confused too, they are suggesting vacuum leak, water coolant temp sensor or MAF.

Thanks in advance for any advice.

Rob VN

You might check both plenum to intake manifold rubber connectors/hoses on bank 1. They have hose clamps on them. Also check the bank 1 hose connection to the AOS. Since your problem seems to be bank 1 that may mean the AOS is ok. You could try cleaning the MAF too but that is common to both banks. Last thought is the Bank 1 catalytic converter on its way out ( loose pieces inside when tapped from outside ). And check all the vacuum hoses for cracks. Good luck.

Bprince_92

Thanks for the reply!
Just thought I'd give an update.
Car was checked by my indie and they can see the stored misfire codes but they couldn't get the car to msifire even on a cold start (they kept the car overnight). They said there were no obvious vacuum leaks but a couple of hoses were slightly loose so they tightened them. They also cleaned the MAF.
Their thoughts are that this is a MAF issue and will get worse at which time the diagnosis of a MAF failure will be more obvious and I should change it. For now they said just to keep driving it as per normal and that I won't be causing any long term damage.
I'll update the post again a bit later to see if a clean of the MAF and tightening hoses has helped at all.