Hello,

I have a 2004 C4S convertible w/ 94k. I've only owned it for a few months, but purchased it knowing of a few things it needed. I've replaced the clutch, IMS, RMS, oil filler tube (cracked), and a couple other misc things.

MY PROBLEM:
Every morning after it's sat overnight (or even at work after it's cooled down after a few hours) it will almost ALWAYS sputter and will sometimes die right after initial startup.

I did an induction and injection cleaning service which truly seemed to fix the problem for about a week, but it's back!!!

I've seen similar posts about the Air Oil Separator on other ones, but my symptoms seem to be different than those posts.

I asked my Porsche dealer if I needed new plugs/injectors/coils and they said they'd actually start by testing the MAF.

Any ideas?

Thanks!

 

Reads like a temp sensor input is off and the fueling starts out too lean.

'course the symptom description is a bit vague. The mixture could be too rich.

Does the engine start ok when hot? A too rich mixture generally causes problems when the engine is hot while a too rich mixture when the engine is cold is less likely to cause problems.

You need a scan tool to view the coolant and the intake air temperatures at cold start and right after. These should be close to the same and should be close to ambient.

They should also continue to agree as the engine starts and begins to run though shortly after the engine begins to run the coolant temp will climb approx 2 degs every second while the intake temperature should remain close to ambient.

If you want to get your hands dirty disconnect the MAF at the wiring harness and use the scan tool to erase DTCs. Even though there are none this resets the fuel trims among other things to their defaults.

Then under similar conditions start the engine and see if the engine behaves the same. If it does then the MAF is probably not the problem. If the engine doesn't behave the same then reconnect the MAF, clear the codes again, and do the test again. If the engine then behaves as before the MAF was disconnected the MAF is probably the problem.

Treat that MAF with care. Static discharge into its connector or the connector it plugs into and you could be buying a new MAF even though it was ok before you zapped it. Or you could be on the hook for a new DME.

Or take the car in. The tech can hook up the diagnostics computer and check the MAF signals for any signs of problems and eliminate other possible causes of the symptoms. Sometimes an hour of diagnostics saves a lot more time and money than it costs.

 

Sounds like you may have a vacuum leak. Makes it too lean when cold.
Did you deploy the roll bars? If so could you post more pics?

 

If you join your search would include all areas of Rennlist instead of only visitor areas.

 

Starts perfectly when the car is warm

 

Thanks and good to know. Any input on my challenge?

 

Does it continue to idle rough or does it settle down after warmup? Do you have any codes? Any other information would be helpful. Sputtering on startup can have an AWFUL lot of causes and on a higher mileage vehicle it's usually a combination of things.

 

Thanks for the reply. It settles down after only about 3-5 seconds once it's actually fired up and started.
If I give it ANY throttle, literally any, while it is sputtering, it will instantly die.

After it stops sputtering/starts properly, it is perfectly fine. It's just annoying as hell (and somewhat embarrassing when others are around) when I get in my car to start it after its been sitting for a while.

I'll try to take a video tomorrow am when I start it up. Possibly later today too

 

Sounds to me you have one or two leaking injectors. They drip amd flood the cylinder when it sits for a long time.

 

^^^ this

I have a cold start stumble for the better parts of 8 months. After Porsche looked at it a half dozen times, they finally changes 2 injectors and it's fine now.

 

Although a video may be helpful, we're gonna need those codes (or lack thereof). If you don't have a reader the nearest auto parts store will do it for free. I would definitely do Macster's procedure for checking the MAF as well. That's a great write-up.

 

There are no DTCs that a generic scan tool shows. Also no check engine light.
Im sure the PORSCHE specific diagnostic may pull some, but my cheapie does not

 

Hmm, maybe try techron injector cleaner? How is the battery voltage?

 

Not surprised. We're going to need to track misfires though (assuming it's not the MAF)

 

A leaky fuel pump internal check-valve could cause this.