engine stall issue

1999 996 C2 hard top 6 speed. Hey guys I have had a stall issue for the past few months that has yet to be solved. Sometimes when the engine is warm it will stall for 1 second or less then spring back to life. it seems to happen regularly for a while then not at all for a while. I have replace the mass air flow sensor and the crank position sensor. The engine is throwing no codes and I have had the fuel pressure checked at the rails and it is fine. I thought maybe Cam position sensors but someone told me those throw codes. Any ideas?

Ignition switch?

switch ordered, we'll see if thats it Thank you,

Have you cleaned the idle control valve?

ignition switch replaced, idle control valve cleaned stall persists

Did you use a 9v battery to operate the control valve when cleaning it? It's much more thorough that way. Have you replaced the fuel filer and air filter? Do you have Durametric?

Plug up an Obd2 and monitor fuel trims , if the trim starts going rich right before it stalls your 02sensors are aged. When the 02sensors are aged they will cool off at idle and momentarily stop working cause fuel trim to start going rich and engine will stall before rich limit is reached or code set..Then after restarting and reving engine 02sensor heats up and starts working again...

Got it, I have a (fancier than mine) scan tool on the way. And probably replace o2 sensors anyway. Thanks!

Update: The fancier scan tool showed a pending MAF code. Which is the same code shown before replacing the MAF with a new Bosch unit a few months ago. Hooked up the positive terminal in the engine bay to an oscilloscope and the signal had some spikes. I can upload a vid of the Scope if that might help.

Yea, lets see the scope...

Hey guys, I have not been able to find a video format that rennlist will accept that also shows the green on the scope. I will try again tomorrow

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Hope this works

Maybe this: https://www.youtube.com/watch?v=kHE3...ature=youtu.be

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You need to refine your scope settings for more detail, I can barely see the alternator ripple, anyway I would probably look elsewhere. Unplug your idle speed control, it should barely idle at about 500-550rpm. if it dies you may need to clean the TB better or adjust the hard stop...( the hard stop should never need resetting, but sometimes people mess with it or it gets bent).. Also watch your fuel trims carefully to see if they are changing a lot...

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will do, thanks

Really don't need the scope. The MAF outputs a DC voltage. All you need is to log the MAF voltage using a Durametric. Any signal drop/spike will show up in the logs.

We purchased our 2002 tiptronic about a month ago 300 miles from home, now have around 750 miles on it, and it received a major service at a Porsche dealer including plugs and coils and test drive by an independent shop, both said everything was good. When I was driving home from the initial purchase all normal, when wife behind the wheel while on freeway maybe two times there was a firm thump seemingly from the transmission, and we thought it was because she is inexperienced she rapidly pushed the throttle in and out. Later when home she started it and got a check engine light, using my basic code reader I think it said misfire and I cleared it, and we thought it might be an anomaly because of the way she started it. A few days later I was in heavy traffic on a multi-lane freeway on ramp at low rpm and it died with all the warning lamps coming on (like when engine is off but key is in). I might have been gently applying the brakes, and the ac was on, I understand those can be factors because they put a load on the engine and electrical system. Very luckily on the third crank it started and I was able to get out of that dangerous situation, and there was no check engine light. This morning when driving in to work cruising on the freeway with throttle not being pushed in our out, a very firm drivetrain thump and check engine light comes on, then everything returns to normal. I mention all this because all factors need to be taken into account when troubleshooting, and symptoms may stem from one or more separate problems. When I get home I'll find my better code reader and we'll see what the code is.

P0335 code twice now, once when starting and once on freeway along with a firm "thump" seemingly from the transmission. Also engine dies while idling and restarts after two or three cranks. Apparently entire ignition is very intermittently turning off and reading the threads need to look at the Crank Position Sensor (CPS) and associated wiring to engine computer, and possibly just replace the sensor and carefully ohm out and inspect the wiring for corrosion. Our 2002 100k mile C2 has been in Arizona and North California and is clean so don't expect corrosion in wiring.

Have you checked the oil cap? Seal might have gone on that. Oil filler neck might not be sealed correctly. All could cause a not so nice idle.

Indy replaced CPS ($175 sensor $325 labor Tip not manual). After 16 drive cycles no P0335 no die at idle and no drivetrain thump cruising on freeway.

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Glad you got your issue fixed and reported the outcome. The OP had already replaced his CPS as indicated in the first post, we have not heard any update on his issue yet...