Davebrossi

I feel I should start by saying that before taking delivery of my 986 I had a PPI performed and in addition to decent compression, analysis of the oil showed no metal filings or anything else to hint at a forthcoming IMS bearing failure. The car doesn't leak oil, and I've put 1400 miles on it since taking delivery. That being said....


Yesterday I went to start the 986 up after a couple days of sitting. Of late I've noticed that when the car starts up cold, the idle seems to bounce a bit and the engine seems rough briefly before settling into 1000 RPM in what I assume is the proper warm up process. While this has been of concern, it pales in comparison to a loud 'Pop' I heard shortly after turning the car on yesterday. I shut the ignition off and climbed out to look around, there's no debrey or bits of anything, no puddle, etc, and the pop sounded like an amplified version of the metallic 'tic' you hear when metal is cooling down. It only happened once, and after a minute or so I was a regular idiot and drove the car less than a mile during which time nothing seemed amiss. When the car is idling it sounds fine, a lifter might be a bit sticky, but there's no grinding noise, no 'jet engine' wine (other than the sound of the belts which I've heard on two 968s, etc) and no rattle or any other sound to make me think I'm about to need a new engine.

Any thoughts? My familiarity is with 968s and my BMW, and the 986 engine is still a bit of a mystery. Not afraid of tearing into things though! Thanks!

...Oh, and how do I go about resetting the airbag indicator?

Macster

The out of character bouncing idle and rough idle at start up and the pop are probably related.

Generally, an intake pop or backfire through the intake is a sign the mixture's lean. If the backfire is out the exhaust this is a sign the mixture's rich.

Now there could be an intake air leak. It is not too bad but at idle the air let in via the leak represents a considerable portion of the total air the engine's ingesting and the symptoms are more severe at cold start/idle.

There may be no CEL, no error codes, because cold the DME is not yet in closed loop mode and by the time it is the engine is warm enough and the mixture is near right enough that the condition will not trigger a CEL/error code.

'course if it is an air leak this can be the early warning signs of a failing AOS, or it could be just a bad oil tube filler cap or a crack in the oil filler tube. A leaking air intake leak is rare, unless you tell me the car's been worked on in that area recently.

Another possible cause can be the coolant or intake air temp sensor (MAF) is optimistic on the temperature and the result is the DME supplies too lean a mixture.

My money would be on a sensor. If an air leak was present I think the CEL would have come on and there would be one or more error codes pointing to a lean (or rich) operating condition. (But a failing AOS can sometimes act up and the CEL remains off.)

When my 02 Boxster's oil tube filler cap developed a leak -- though this hadn't been diagnosed yet -- error codes appeared that had me suspecting the MAF. the original MAF. In fact I replaced it only to learn the cause was the oil filler tube cap leaking when the error codes reappeared and I was looking over the car with the engine idling a co-worker heard the cap leaking. (I'm hard of hearing.) (The good news is I had saved the original MAF and when the replacement MAF failed after nearly 100K miles I reinstalled the original MAF and it is working just fine to this day...)

Anyhow, unless you're willing to get your hands dirty that's about it.

Oh, airbag warning light. A dealer or a well-equipped indy shop can read the codes and of course clear them and extinguish the warning light.

But you really should know why the warning light is on -- it is after a 'warning light' -- and if there's a real problem have it fixed.

Sincerely,

Macster.

Davebrossi

Hi Macster,

The Airbag warning is my fault. I removed the seats to clean the interior (I know, there's clean and then there's my brand of 'neurotic clean') and left the passenger's seat out on the drive to the self wash. The airbag warning light tripped then. I'll take a look at the oil filler cap at idle to see if we've got any hissing or a strong vacuum. I do own a Harbour Freight OBDII reader, but no codes nor a CEL yet. Glad to hear it's not impending engine disaster though! :-) Thanks again!

smlporsche

Do you have anything but the stock air filter on it? If it is the stock set up how long since it has been changed?
The reason I'm asking is that the idle fluctuation is perhaps the sign of a dirty Mass Airflow Sensor (MAF).

This can be cleaned with the proper MAF cleaner like this..
Just be careful as it is sensitive.

Tinbit

Mine has a similar idle bounce on cold start, it lasts maybe one or two seconds. My PPI revealed a slightly cracked oil filler tube which I haven't gotten around to replacing. After reading this thread it seems those two items may be related.

Davebrossi

Hi Eddie;
I do not know when the filter was last changed. It'd be worth checking into however as it's another excuse to dig into the engine.

Tinbit; how difficult is an inspection of the oil filler tube?

Byprodriver

Dave welcome to the wonderfull world of Boxsters! Sounds to me like you would prefer to reset that airbag light yourself. Checkout the Durametric diagnostic software.

bar10dah

Yes, definitely worth the investment to start out with a fresh oil/filter change. Not only will you ensure the right oil is used, but you also take away the question as to how long that old oil has been in the car. When I bought the car, I was told it just had an oil change. But, they couldn't tell me the brand/weight of the oil. So, I changed it again myself.

Depends on the damage. If it's a small crack, you may not be able to see it. Best way is with a small mirror, so you can look at the undersides of the tube, where it generally cracks. Also, look for traces of a leak by running your hands around the tube. If your fingers come out with oil on it, more than likely it has a leak. Mine was leaking from as far back as the rear firewall. Couldn't see it from the top of the engine, but I could feel the old caked on oil on the underneath of the tube. After I pulled the tube out, noticed the end which connects to the rear firewall was folded over and not providing a good seal. So, not cracked, but still causing a vacuum leak.

nemo9xx

Thanks Macster, by reading your message I found my problem on my boxster..... I forgot to put back the engine oil cap

Macster

You're welcome.

BTW, I've left the oil tube filler cap off once or twice. A funny faint honking/moaning noise under some operating conditions, and then later when I open the trunk the big huge gaping hole that is the oil filler tube is staring me in the face. And the oil filler tube cap is laying on the trunk carpet mocking me.

Embarrassing. But thankfully apparently harmless. The best kind of mistakes.

Sincerely,

Macster.

nemo9xx

;-) same thing for me (for the noise) , at 4000 RPM the sound of the engine sound like if I have a 2 inch hole in the exhaust system absolutely destabilizing ??$$$$$$$

thanks again :-)

Davebrossi

Update: I performed the basic cap test and noticed a rougher idling engine with the cap removed. I spoke to a 993 owner who stated it sounded like a problem he's been having with his Varioram system. Does the 986 incorporate this setup? Also got a Durametric setup, what a fantastic piece of software! Noticed the cam derivation and wanted to know where to get more information on what is considered normal with that.

paradigm79

In short, it doesn't have Varioram it has Variocam, and there are few different versions out there. What year is your car?

You can watch cam deviation and you can also watch actual cam angle. The general rule for cam deviation is its value doesn't matter so much (within reason, I think + or - 6 degrees for your car...someone correct me) so long as it doesn't fluctuate at idle. That check generally pertains to the health of your IMS bearing, not variocam.

Watching actual cam angle compared to requested cam angle may give you some indication if the variocam is acting correctly. The DME requests an angle and the actual angle should match it. Ultimately the system utilizes oil pressure to actuate the change in cam angle, so even if the solenoid that controls it works ok, if there is any issue with oil pressure it could affect proper variocam function.

I may be fighting a similar issue, please let us know what you find.

bar10dah

With Durametric, how can you verify that the variocam is working correctly?

Macster

Can't help you with the Durametric question, but it looks like someone else has given you a good response.

Removing the cap is really only a viable test in the context of a suspected AOS.

What I found when trouble shooting what turned out to be a bad AOS was at idle while I could unscrew the cap I could not remove it. The engine's internal pressure was very low -- due to the bad AOS -- and I could not remove the cap against this pressure difference.

(In severe cases -- my engine was probably close -- the engine can pull air past the RMS -- this can make a noise -- or crack a weakened oil filler tube. Oil in vapor form can be sucked out of the engine and the engine will smoke and stumble and near the end, too close to the engine being at risk of hydraulic lock, liquid oil can drip from the exhaust outlets.)

Absent a suspected AOS, if the engine is basically healthy, removing the cap creates a big air intake leak at least at idle. At higher rpms the amount of air that air that is available to enter this 'hole' is limited and the engine will not manifest any symptoms from this leak. Short term and long term fuel trims though will most likely be affected.

Anyhow, remove the cap and the engine will react and run rough and rpms may dip. The DME will very quickly adapt though and the engine should smooth up some. It may not regain 100% of its previous idle smoothness though.

When the cap is replaced this of course removes the intake air leak and the engine can react again, though my experience is not as dramatically. (It is one thing for an engine to go from a just right mixture to a too lean mixture and another for an engine to go from maybe a bit lean mixture to a too rich mixture.)

Anyhow, the DME will once again adapt and the engine should now regain its previous/original idle smoothness.

Sincerely,

Macster.