kj217

at traffic lights, the rpm somtimes goes down to 100 rev and the engine oil light pops up for a second then the idle goes back up to normal.
What can cause this?
How to fix?

Shark Attack

The oil light comes on becasue the idle drops to low to pump the oil.. Fix the idle and you will fix the pressure thing.




Ok Seriously


on the 928 this is caused by the Idle air stabilizer. Not sure if we have one on the 996.

Macster

What Shark Attack said. To add eliminate the AOS. One AOS failure mode can cause the RPMs to fluctuate over a few seconds period -- drop then climb and repeat -- and as the rpms drop oil pressure drops cause oil pressure related to how fast engine spinning.

Sincerely,

Macster.

10 GT3

Strong recommendation to get it into your dealer ASAP. The oil pump on the head that drives off the cam sprocket has been known to fail. If not corrected immediately it can mean a new engine.

ivangene

Sorry, but that is just not the case with OP's car. Its got a running issue that causes the presure to drop - its rpm related and not a mechanical concern.

The same thing can happen in summer w/o the idle issue if you run light oils.

Your idle needs to be fixed and I am not the best at those. Might be a vacuum leak, an AOS, a sensor issue, dirty MAF or throttle body. You need to diagnos it and fix it, the oil issue will be gone - as long as you run good oil too

redridge

what year? check the ICV and throttle body.... they might be sticking and need cleaning.... and clean you MAF.

kj217

its a 00 C2.
where is the ICV located?
How to clean it?

pszikla

I think that only the '99's have the ICV. Once they went with electronic throttle it was eliminated.
On the '99 it is on the side of the throttle body, and you can use carb cleaner to spray around inside of pivot points of moving plate. Easier to clean if you remove it. (2 screws)
Pete

eclou

if it is an 00 I would guess the AOS is going out if it has not already gone out. If it never has been replaced I would do so anyway and then clean your MAF and throttle body as the oil residue will lead to errors in the MAF readings and gumming of the throttle plate.

kj217

i did the oil cap test and AOS seems to be ok. i also cleaned both MAF and TB eventhough they looked clean to me in the first place.
the car went out a major service in the dealer where they changed spark plugs and flush the fuel system.
The car run like a breeze except for that drop at full stop and trans on N.

Please, help.

Macster

The check for excessive vacuum at the oil filler tube is not 100% conclusive the AOS is ok.

There are at least 2 failure modes the AOS can experience and they differ in the symptoms they manifest.

IOWs, had you found excessive vacuum at the oil filler tube opening that would have confirmed the AOS was bad. That you didn't find this vacuum does not eliminate the AOS from consideration.

The cars (2000 and newer) equipped with E-Gas do not have an idle control valve. The E-Gas system controls the engine's idle speed.

I don't think this will help, but follow the instructions in the owners manual regarding disconnecting the battery, as if you were going to replace the battery.

Before you disconnect the battery note the radio's security code. Be sure all major electrical loads are removed. Do not leave the head lights on for instance. Turn the key to the off position and remove the key from the ignition switch.

Disconnect the battery. Wait some time. Minutes is probably too much time, but what the heck.

Reconnect the battery.

Now let the E-Gas perform a recalibration of its internal circuits. This is done automatically after a battery disconnect when you turn the ignition key on and wait at least 10 seconds *before* starting the engine.

You'll have to re-enter the radio's security code and reset the window stops as well after you reconnect the battery.

If this sees the idle now stable and remaining so great. I don't think it will help but you might consider trying it.

But if this doesn't help it may convince you the cause of the symptom lies elsewhere.

I've not heard of this as a problem with Porsches but in some cars the A/C compressor engaged switch/sensor can act up and "fool" the engine controller into thinking the compressor is on when it is off or off when it is on.

This causes the engine controller to attempt to adapt to the expected increase in parasitic engine load by slightly increasing the engine speed. Then the engine controller recognizes the engine speed at idle too high and it backs the speed down again to the nominal idle speed.

The result in the engine's idle speed varies by some noticable but usually small amount but varies by more than the idle speed should vary under normal operating conditions and when everything's working just fine.

Not sure what you can do about the above. Trouble-shooting this generally requires the use of the PST2 (Porsche System Tester 2) diagnostics computer to monitor the MAF and the engine idle speed and the presence/absence of parasitic engine load signals to the engine controller.

If you haven't already done so, you can try this: Disconnect the MAF at the wiring harness. Do not remove the MAF from teh intake pipe.

Ideally you want the engine dead cold. Now when you start the engine with the MAF disconnected the engine may behave a bit different cause it will have been used to having the MAF present and supplying the engine controller the amount of air the engine is using.

Start the engine and let it idle and warm up and then drive the car as you do when the idle symptom appears. The idea is to as close as possible duplicate the same conditions with the MAF disconnected as when it was connected.

Try your best, give the engine every opportunity to manifest the symptom. Try to avoid treating the car the engine any different than you did when the MAF was connected.

If the symptom to the best of your ability does not appear, depending upon how confident you are regarding your efforts to give the symptom the chance to appear, this strongly suggests the MAF at fault.

If the symptom appears then this almost certainly eliminates the MAF from the list of possible sources of the symptom.

Note: With the MAF disconnected the check engine light may come on. You will probably have to clear this error associated with the CEL cause it may not clear on its own after the MAF is reconnected.

Sincerely,

Macster.

kj217

great write up Macster,,
i will follow your instructions and let you know.

Shark Attack

My money is on the MAF. Are you running a stock Air filter?

redridge

check for air intake leaks.... mostly, leaks after the MAF.... if air is coming in after the MAF, then the MAF is not reading the extra air coming in.... just throwing this out there.

kj217

i am running the stock air filter,,
I have disconnected the MAF and the symptom appeared again,,
I am so confused!