Macster

Well, I like to mention that there's a risk to trying to self-diagnosis -- even with the "help" of well-intentioned people on the 'net -- a car acting up and that is the risk of having a relative minor problem turn into a major problem and cause some serious engine damage, maybe even destroy the engine.

With you having no access to any data viewer that allows you to view various engine sensor inputs to the engine controller, and perform other tests, you've gone about as far as you can go.

As I think I mentioned, my 02 Boxster at around 78K miles developed a mlld idle fluctuation with the idle climbing a bit then falling a bit but nothing dramatic and certainly not bad enough to cause the oil light to come on. course, I should mention there was several inches of snow on the ground and while the car was in a garage it was still cold and the engine never got real hot so the oil may not have been hot enough to be thin enough the drop in rpms enough to affect oil pressure.

I messed around and did what I could to identify the source of the problem but when I encountered the high vacuum -- quite by accident -- at the oil filler tube and the engine began to smoke all the time, though not bad, I got scared and called the dealer's service department. Service manager told me "AOS" and to not drive the car, avoid running the engine. Even though I was out of work at the time I still had the car flat bedded to the dealer and had the AOS replaced.

Symptoms gone and for not much money. (In fact while car in for repairs I drove my other car 2000 miles to a job interview -- I hate to fly -- and managed to get a job offer which I accepted. The Porsche rode behind a moving van on an open trailer after getting a new AOS when I moved myself 2000 miles west to take the new job.)

Now even that AOS failed at I forget what mileage -- call it 180K -- and this time failed a bit differently. No idle symptoms, just after hundreds of miles drving in one day -- on a trip -- setting the check engine light. I forget the codes, but decided to press on until the MAF -- I suspected MAF -- failed and I'd limp in and buy a new one at some dealer along the way. But 2 days later upon first engine start of the day the engine smoked like crazy. I knew the problem and had the car flat bedded again to a dealer, the same dealer as it turned out that did the the 1st AOS. This second time instead of having the car flat bedded 40+ miles it was over twice the distance away.

Still money well-spent.

My point is that you have to decide how much longer you're going to fuss around and try to sort of solve this problem without the proper training, without the proper equipement.

I'd love to be able to tell you the problem's the MAF or an air leak, and not the AOS, or even that it the AOS, or something else, but I can't with any confidence. No one that I know can unless he's a tech who's seen enough of these cars and with this symptom to know what it means.

You can elect to continue to use the car and let the symptom progress to where it is more obvious where the problem lies. I do not recommend this technique though I have followed it once or twice for what I suspected to be either MAF or O2 sensor problems. I was wrong on the MAF -- it was a leaking oil filler tube cap -- and right on the sensor. I fixed the car in both cases, though the first "fix" cost me nearly $413. $400 to replace a perfectly good MAF and $13 to replace a bad oil filler tube cap.

However, as I tried to convey with my story about my experience with AOSs, is tha sometimes you need to get the car to an expert and have the matter sorted out. This usually proves to be the least expensive course of action in the long run. And sometimes in the short run as well.

Engine speed dropping low enough to cause the oil light to come on is not good. The engine oiling system is probably fine, the low oil pressure caused by what I suspect is a relatively big drop in rpms.

In this situation the more you run the engine to try to identify the source of the problem the more risk you take that each time the oil pressure drops some bearing wear and tear is taking place, that a cam lobe or lifter face is receiving insufficient oil and wearing or galling.

You could perhaps finally identify the source of the problem -- say it is the AOS and call it a $500 repair bill -- only to find the engine needs new bearings or new cams and lifters cause the low oil pressure ruined them.

My advice is to get the car to a qualified shop staffed with techs who work on these cars day after day and know them inside and out.

And get the car to a shop without driving it.

If you insist on continuing to drive the car, running the engine, then be prepared at any time to if the engine's condition shows or gives any indication it is getting worse to shut the engine off as soon as it is safe to do so -- which I hate to say it but you need to be aware of it may already be too late -- and then get the car flat bedded to a shop.

And this time don't start the engine at all cause there is no more running of the engine that's going to make the situation better, it can only make the situation worse.

Sincerely,

Macster.

kj217

an update,,
i took the car to the dealer,,
they found no codes,,
cleaned the MAF,,
reflash the ECU,,
checked all possible causes,,
chraged me $200,,

later at the same night the car was out,, it happened again and the RPM dropped to 200 revs and back up again,,

i am out of ideas,, please, please, help!
:@

redridge

hmmmm, bad gas? try disconnecting the - battery terminal. Make sure you have the radio codes before you do... this will reset the ecu. Im out of ideas as well.

Macster

Did you think of leaving the car with the dealer (I assume a Porsche dealer?) to have the tech reproduce the symptom? It is very important you relate under what conditions the symptom appears so the tech is successful at reproducing the symptom.

Even though there are no error codes symptoms can be very helpful to a tech in trouble shooting a problem.

Absent any instrumentation to monitor the various sensor inputs -- like short term fuel trims, air flow, timing, intake and coolant temperature, etc. -- you are going to remain in the dark as to what's going on.

Let's recap:

Did you check for excessive crankcase vacuum by trying to remove the oil filler tube cap while engine was idling?

Is the throttle body, its butterfly valve, and the area downstream of the throttle body (the intake manifold) free of any signs of contamination?

Is there any amount of oil present in at the where the connector comes into the manifold behind right after the throttle body?

Is the oil level stable and good or has it dropped any?

Any smoking upon startup or at any other times? (A brief cloud of smoke at cold start especially if you've not run the engine much is ok. But if the cloud persists is not ok.)

Does the symptom appear when the MAF disconnected?

What is the over all condition of the car? Well maintained? Or something less than that. Has fuel filter been changed. Is fuel level ok?

There's not a lot a novice can do beyond trying a few things.

Your best bet is to return the car to the Porsche dealer, or some qualifed indy shop, and have the trouble diagnosed. This requires the tech be able to reproduce the symptom.

I'm leaning towards AOS but I wouldn't want you to replace it solely based on my layman's opinion.

The rpm drop is a bit more severe than I have seen (or read reported) a bad AOS causes. But it is still my 1st choice for the cause of the symptom.

But it could be a fuel supply or fuel pressure problem. Or something else.

To have the car exhibiting the symptom/behavior while at a dealership with the car hooked up to the Porsche diagnostics computer system and to have the various sensors and inputs available a tech should be able to eliminate many things very quickly. Besides the computer the tech has his eyes, ears and fingers to help him: For instance the tech might see the vacuum hoses that run from the AOS to the engine collapse when the rpms drop or he might feel them flex as the engine runs. This would suggest excessive vacuum and provide him a clue.

If you're looking for a definite "this is what's wrong" and then taking this to the dealer and telling the dealer "this is what's worng, fix this" I don't think you're going to get that. I can't/won't say AOS. If I did and you replaced it and it wasn't the AOS I'd feel bad. Worse the problem could get worse and then the car and you'd be worse off than are now.

As I think I've mentioned the problem may not be serious, now. But messing around trying various things, continuously reproducing the symptom when it obviously of no value to you since you are not able to know what it means and for us here the same applies, could be moving the problem towards a more serious level.

There's a risk involved in prolonged self-diagnosis of engine symptoms. Anymore diagnosis I believe should be done by a trained qualified technican and not by you and not for the benefit of anyone here.

Sincerely,

Macster.

kj217

Did you check for excessive crankcase vacuum by trying to remove the oil filler tube cap while engine was idling?
Yes, i can easily remove the oil cap but when removed the rpm fluctuates.

Is the throttle body, its butterfly valve, and the area downstream of the throttle body (the intake manifold) free of any signs of contamination?
No

Is there any amount of oil present in at the where the connector comes into the manifold behind right after the throttle body?
No

Is the oil level stable and good or has it dropped any?
Utterly stable

Any smoking upon startup or at any other times? (A brief cloud of smoke at cold start especially if you've not run the engine much is ok. But if the cloud persists is not ok.)
No Smoke at any time

Does the symptom appear when the MAF disconnected?
Yes

What is the over all condition of the car? Well maintained? Or something less than that. Has fuel filter been changed. Is fuel level ok?
The car is mint condition and regularly maintained. Fuel filter replaced 3 weeks ago

Macster

The idle will change when the oil filler tube cap removed. The idle should stabilize though in a moment or two.

And when you replace the cap the idle will again change and again it should stabilize and recover nicely to what it was before the cap removed and then replaced.

The absence of other warning signals of pending AOS trouble lowers the odds it is AOS.

I''m running out of ideas.

All I can think to ask now is: Was the symptom present before the fuel filter changed, or did it appear after?

Sincerely,

Macster.

kj217

the symptom was there before changing the fuel filter,,
Loren is suspecting the throttle body positioner,, what do you think?

Pac996

What is your idle when cold starting?
What's the idle after warmed up?
Is your a/c on?
What's the weather?
What is the fuel level?
Do you run your fuel tank around 1/4 before refueling?

Most important is not running the gas tank past 1/4 is a fair warning.
Modern electric fuel pumps need constant fuel around them to stay cool.
They burn out quick if sucking air and not bathed in liquid.
Could be a weak fuel pump, water from winter storage or whatevers.
If its the pump you'll know it when it finally goes which might take a year.

Oh yah, does the idle run up higher than normal idle when jumping back up?

Macster

Let's see.. Car is a 2000? IIRC that is the 1st year E-Gas (throttle by wire) available.

Sure. E-Gas (pedal) could be acting up or the electro-mechanical device (throttle body positioner) on the side of the throttle body that moves the butterfly valve on command by the engine controller from the inputs it receives from the E-Gas pedel potentiometers.

Both the E-Gas and the throttle body positioner are pretty sophisticated devices and should lend themselves well to proper diagnostics by some shop equipped with the proper Porsche diagnostics computer.

There may be more less high tech ways to trouble shoot either of these devices but I don't know of any off hand.

In short Loren's suggestion makes very good sense and you would do well to eliminate either device as the cause of the symptoms you see.

Which still leaves you facing taking the car to a qualified shop that is set up to diagnose these items.

Sincerely,

Macster.

kj217

What is your idle when cold starting?
around 900,, i believe it should jump over 1000 when cold starting,, but it doesn't,,

What's the idle after warmed up?
around 700

Is your a/c on?
a/c is off but not showing OFF in climate display

What's the weather?
30c 40-50% humidity

What is the fuel level?
fuel level is ok

Oh yah, does the idle run up higher than normal idle when jumping back up?
didn't get that!

Pac996

Couldn't think of saying does your rpm's roller coaster up and down searching out where to stabilize. I'm thinking if it is roller coastering I would forget about it being a throttle control related problem and go after air fuel systems. MAF, fuel pump, fuel, or the elctronics sensing something that says to increase throttle.

kj217

well,, when it drops, it doesn't jump back up,, it goes back up slowly to normal,,
i must say that my car doesn't have this symptom all the time,, it happens mainly after long rides,,

kj217

i can't recall that the rpm stabilized until i put the cap back in place.

Graufuchs

Does this car have a throttle body alignment feature? I recall with the audis, if you disconnect the battery and reconnect, you turn the key to the acces position and the throttle body aligns itself.

kj217

a thought,, everytime the rpm drops,, a sound of an electrical actuator occurs a moment before the drop,, this sound comes from the front right behind the dashboard,, it is the same sound that happens when you turn the key to ON position before a cold start,,
I am starting to suspect the fuel pump now but,, a weak pump should affect the overall performance of the car,, right??