TroyN

I've had a condition that has gotten worse in the last week or so. Now at cold start the car will idle low and roughly, will make popping (like backfiring) sounds and runs rich. Tonight I let it run for maybe a couple of minutes and then suddenly it stabilized itself, idle speed went up a 100 or so RPM and all was well.

When it's doing its poor idle thing, I just touch the gas pedal and it will drop RPM and then recover. Strange, I had the same problem on my '87 Scirocco with CIS, though it never quite went away so not sure of the solution there. I had checked cold start valve, temperature sensor, etc. to no avail, not that it's relevant to the Boxster.

Anyway, ideas? Saw posts RE: MAF, but not clear on whether MAF problem affects all conditions, i.e. not just idle and not just cold start. Again, once its warmed up, and not even really warm, just 2-ish minutes warm, it runs great.

Thanks in advance for any help.

Tierce

secondary air pump maybe? Just an idea, considering I haven't had this problem before.

the air pump only runs when the engine is cold. I believe it injects air into the exhaust to help control emissions when cold, but if it's not working, and the exhaust gas mixture is wrong, the computer will not adjust the air/fuel mixture correctly, and it will run rough.

like I said, just an option, guys, correct me if I'm wrong.

99firehawk

no not he secondary air pump, it is fr emmisions only and wil not affect driveability in any way

TroyN

So far my issue hasn't affected driveability, it's only the first few minutes after a cold start. Anyway, I took it to the dealer today, they didn't find anything wrong. Not sure if I trust them though. They suggested running fuel system cleaner through. I thought that was reasonable considering the car wasn't doing this before winter, just after sitting all winter (frickin' snow and cold this year!). We'll see what happens.

cdodkin

You run a battery maintainer over the winter?

Just a thought - low battery means your alternator is working hard to charge it up, and sitting at idle this may be causing some symptoms.

Macster

and hesitation when engine cold.

Lean mixture at cold start can be coolant temperature sensor failure that causes engine controller to believe engine's warmer than it is and thus not enrichen the mixture properly for the actual colder temperature of the engine.

(But it can be tricky: If real cold bad coolant temperature sensor will indicate warmer than actual temperature and engine gets a lean mixture. If just mildly cool, bad sensor an indicate a colder than actual temperature and engine gets a richer mixture than called for.)

Also, low fuel pressure (or insufficient fuel flow but at idle?) will result in a lean condition as the engine controller depends upon a certain fuel pressure and delivery capability when controlling fuel injector widths.

If engine truely running rich -- though a cold misfiring engine can smell "rich" because alot of unburned fuel is making it through engine and cold converters -- suspect leaking injector. Trouble is engine controller will detect overly rich condition on that bank and lean all injectors out. The cylinders of the injectors that are working will thus be overly lean and engine can still exhibit signs of lean running (which is the case) but because of one very bad injector feeding way too much fuel to one cylinder.

The offending cylinder can be id'd by -- with proper diagnostic equipment -- shutting off each cylinder (injector/spark) in turn and noting which cylinder shutoff drops RPMs the least. This indicates the bad cylinder since it is contributing less to the engine's output than the other properly functioning cylinders.

Don't know history of car and how you use it, but a bottle or two of Techron may be called for.

Sincerely,

Macster.

Scwired

Hi,
Was there ever a solution to this problem of rough start when cold? I have had the issue since buying car. Every sensor and part has been replaced, engine fogged and no vacuum leaks, all 6 fuel injectors replaced, eco was checked and came back fine, the ecu would not accept a reprogram from porsche and still will not start and engine floods when cold about 50 degrees or less. I have spent a ton of money at dealers and they "can't find an issue to fix as they don't know what to do". When ambient temp is warm car runs awesome. Any input would be appreciated!
Thanks,
Steve

Schnell Gelb

If you mention your location maybe we ca find you a competent ,honest Indie ?
Meanwhile ,try disconnecting the MAF temporarily.It is easy,non-intrusive and costs nothing.
As Macster hinted - have you replaced the CTS ?

Macster

How do you know the "engine" floods when cold? There will be a strong odor of raw gasoline even from a healthy engine at cold start. This is normal.

If the engine backfires from the exhaust this is a sign of an overly rich mixture.

The mixture is overly rich at cold start on purpose because a cold engine needs a bit more fuel than normal and to provide extra/excess fuel in the exhaust to combine with the air injected by the secondary air injection pump so the extra fuel burns in the exhaust and helps heat up the converters faster. Not all the extra fuel can be injected at the normal fuel injection time but instead can be injected later so the extra fuel is just carried along by the exhaust gases out the exhaust port. Injecting the fuel then ensures there is still some flame which will ignite the fuel.

I don't really hear any backfiring from my Boxster at cold start but with my 996 Turbo I do hear some faint backfires for a few moments after cold start.

If the engine spits through the intake -- probably hard to observe given how buried the intake inlet is -- this is a sign the engine is running lean. Lean during the actual combustion phase.

Best thing I can suggest is if you want to tackle this yourself you need to get a good OBD2 code reader/data viewer/data logger and use it to check the intake air temperature and coolant temperature *before* starting the engine and as it cranks and starts and idles.

What you are initially looking for is an air temperature or coolant temperature sensor reading that is in disagreement with the ambient temperature or each other.