Engine Stall Issue - Calibration Fix?

The Sprint Booster mentioned in tekkie's upgrade thread got me thinking. I have stalled my car 4 or 5 times in the last 5 weeks that I have been driving it almost daily (vacation in FL). Stalled abruptly like driving a car with a light weight flywheel (which mine does not have). Start off with very light throttle and just as you begin to get clutch engagement and squeeze the throttle, the engine stops. I am now wondering if there is a dead zone in the drive by wire throttle that aggravates this? Of course, could just be me....but is there a calibration that could be done to ensure it is working correctly? I know about the E-gas calibration but would Durametric reveal anything that could be improved to cure this? I would be all over the Sprint Booster option if it were $75 instead of $250. I cleaned the MAF about 2000 miles ago just as a preventive measure and the car runs great but this stall situation is both embarrassing and potentially dangerous.

After the event it would only show a Pending or actual code. If you had Durametric connected during the event on the "Actual Values" menu ,you may see something on a freeze frame but that isn't practical- unless you know how to provoke the stall? It sounds(speculatively) like a 'dead' segment of a potentiometer.

e-gas calibration is the only think I know of that you can do. You could watch the throttle % using Durametric (or Torque) to look for wonkiness in the pot. Check for vacuum leaks. Even small leaks can affect idling and make it easier to stall. Is the car hunting at idle more than usual? If you are a PCA member and/or have other 996 buddies, it might be worth driving another 996 to compare it to yours...

I would say no to the "dead zone". It is more about driving style and feel. Of course stalling is embarrassing so practice your take off. Find a nice empty parking lot and do it time and time again. Finding that sweet spot in starting off the line is more feel than science. My car, 99 C2 drive by wire, in Florida, has a feel to it on take off. Don't be afraid to rev it to 1700-1800 RPM and gently let out the clutch while you feel it take off, then bang, full clutch engage and nail it. It won't stall.

OP, is this a new condition or how it's always worked for you? I thought it was the former, but after rereading, I'm not sure

When I am home in NC, I drive the car on nice days in the mountains. With gusto. Not much traffic or stop and go. This past several weeks it is FL in Winter so all stop/go city driving. Which is to say I don't know when this started but I didn't have this issue last Winter in FL with the car so I am thinking something is different. I did do a lot of work on the car in between FL trips - the full menu of mechanical stuff - but I don't see how that would affect this and, again, the car runs great. And idles steady at 700 RPM when warm. I've been driving a stick shift car for about 54 years now so I don't think it is technique. If it only happened once or twice, I would say I just didn't give it enough revs but 5 or 6 times I'm thinking something isn't 100% in terms of throttle response (or something?). The "pot" is part of the throttle position sensor? Is there one of these? If so, can it be cleaned?

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This is why in Post 2 I mentioned "Potentiometer" This link may help - it is Boxster but the same idea. http://986forum.com/forums/diy-proje...l-service.html If you are near Fort Lauderdale - ask Pedro.You'll like him ! http://www.pedrosgarage.com/Site/Technolab.html Google Maps Places http://986forum.com/forums/diy-proje...l-service.html

Is it possible something to do with the clutch? I'm pretty sure it's not your gas pedal position sensor because it has two potentiometers inside that return two different (but correlated) values to the DME so the DME can detect any abnormalities or signal break for the whole travel range of the pedal.

The clutch is new and feels fine to me but maybe the engagement point is a little sharper now? Or perhaps trying to do a smooth but slow start in traffic without slipping the clutch is the root cause. You know, trying not to use too many revs to avoid slipping the clutch. I am going to repeat the E-gas thing since it doesn't sound like there is any test or part replacement that is obvious for this issue. I am back in NC, and if I have issues with it stalling here I may have to dig deeper. Really appreciate all the input on this. I will say, now that I have been paying attention to this, that the throttle response right off idle doesn't seem matched to the pedal movement - seems slow or "late". Which is why the Sprint Booster caught my attention.

My clutch was brand new when I got the car. The engagement point was sharper, I'd disengage the clutch at lower revs to avoid jerkiness and burnt rubber smell. I stalled here and there getting used to it. 5K miles into, I'm much more liberal with the revs out of 1st and much less stalling (still have the occasional brain fart).

Does the duration of the stop seem to matter? If I remember correctly there is a switch that detects if the clutch is depressed - if it's held more than a certain duration (4 seconds I think) the throttle remaps to make starting smoother. For people accustomed to driving a manual this can take some getting used to. There are a few threads where people have zip tied the switch in order to disable the 'feature' - everyone that has done it seems to swear by it. If it makes you feel better I've stalled mine more than any other car I've owned. I'm planning on trying the zip tie trick soon to see if it helps.

Interesting. Yes, I would say it happens after the clutch has been on the floor for a while. Waiting for a gap in traffic to pull out or waiting at a stop light for the blue hairs in front of me to get going after the light turns green. So is this the same clutch pedal switch that you activate to start the car? If so, mine has not been working properly so I had it bypassed but I replaced it with a new one while in FL. A clue?

IIRC one can do an E-gas calibration then with the proper diagnostics computer (either the factory one or Durametric I believe also supports this) check for any E-gas errors. Likely you'll find the E-Gas is ok. I read a post above that you hold the clutch in a while under some circumstances? I would urge you to adopt a driving technique that has you leave the transmission in neutral and the clutch pedal released whenever possible. The only time I actually depress the clutch when the car is stopped is when it is time to shift into gear (1st/reverse) and get the car moving. I never sit at a light or in traffic with the clutch pedal depressed. Also, I have to stress it is important to flush and bleed not only the brake hydraulic system fluid but the clutch hydraulic system fluid every 2 years. As I have reported my experience in letting this go results in an impossible to work smoothly clutch and even though I fully depress the clutch pedal shifting no longer is smooth. Two times now -- the most recent one was after having the Boxster's rear brakes done a few weeks back -- a brake/clutch fluid flush/bleed has made a noticeable improvement in the clutch's action and in the car's shifting.

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Good question. I would be inclined to think its a different switch, since people are able to bypass it without ill effect during startup. In fact, does the clutch pedal need to be depressed to start? I'm not sure I've ever tried. My rudimentary understanding is that there is a switch that is depressed when the pedal is up (clutch engaged). When you push the pedal, it releases the switch. Once the switch is up for 4 seconds, the throttle remaps to make it less sensitive for starting from a stop. The result is a confusing throttle feel in my opinion. I actually stalled yesterday in a parking lot try to do some very slow speed maneuvering around someone that didn't know how to drive/park and almost hit me. I believe I had the clutch in a state of full disengagement or only partially engaged throughout the encounter, which probably lasted more than 4 seconds - then, when I tried to start off I stalled. I know there is a thread that addresses this somewhere. Apparently its a 5 minute job to zip tie the switch in the down position and easy to reverse (just clip the zip tie) if you don't like it or it doesn't fix the issue.