greencalex

Hi All,

So since I got my 2003, I've felt that the car was unusually easy to stall, and not just in the usual "lugging" way, but also in a fashion where easing off the clutch without applying any throttle (or applying the throttle a little late) would see the engine just calmly cut-out.

I've been shrugging this off to the slightly grabby nature of the 2.5 clutch that I had put in, but after driving a friend's NA car, I'm starting to think that maybe something is a little amiss. Needless to say, his car does not stall like this.

Another thing I noticed was that if one did stall his car, when you restarted it, it ran as if nothing had happened, whereas on my TT, if you stall it by lifting off the clutch too fast, then on restart, the idle oscillates widely for maybe 10 seconds before settling down to a steady rate.

Do other folks see behavior like the above, or does this sound abnormal?

Has anyone else seen behavior like the above and traced it back to something needing repair?

Under normal driving, everything seems to run fine...

Any thoughts greatly appreciated.

-- Alex

wross996tt

If you list your mods, that would be helpful. If it has a flash for example, you may need to adjust the idle rpm or if you have a LWFW...Secondly have you read your codes?

jeanmarcboilard

Idle up and down sounds like air leak. Mine did that when it had a leak on the turbo inlet.

Atrox

That or your maf/air filter needs attention.

For sake of redundancy do an e gas reset.

911mhawk

Not normal, either is the idle issue, haha

I've killed mine atoo, the clutch master PP gives about a 1 inch range of pedal that necessitates a litte gas right away.

Chris996

If oil pressure gauge is jumping around, replace oil pressure sending unit. Had occasional engine idling too low. Had unit replaced, issued solved. I had to do this on all three of my 996s.

greencalex

Sorry, yeah, I should have given more details.


As far as I know, the only thing not stock is the Sachs 2.5 clutch that I put in.


As I am the third owner, it is possible that there is a tune flashed into it, but the boost seems to top-out around 0.8, so I'm inclined to think that nothing has been done to its programming.


The generic OBD2 reader that I have does not show any codes, but I don't have the ability to read anything Porsche specific.


I once saw it throw a P0001 (Fuel Volume Regulator Control Circuit/Open), but this behavior preceded that occurrence, and I'm pretty sure that the code was because I let the battery drain pretty low.


Oh, and a couple of months ago I had a fuel pump go, and had to have it replaced.


Cut-out stall seems to happen more when it is hot outside.


Right now, the steady state idle is around 800rpm. When it is oscillating, at first it fluctuates between maybe 500rpm and 1700rpm, but the range diminishes quickly, and after 5-10 cycles it goes back to steady state (oscillation frequency is maybe around 1Hz).

greencalex

Air filter is clean.


Am I correct in assuming that disconnecting the battery would do the gas reset? If so, then I've already done that. (pulled the battery to have it tested)

greencalex

There is no doubt that the 2.5 clutch is harder to deal with than the stock clutch, so embarrassment aside, I don't mind the occasional stall.


It is the "just cuts off" stalling behavior that strikes me as so strange. Often when this happens, it feels like one got a perfect take-up because the car just gently starts to move; it is only after one presses into the throttle (and gets nothing) and then glances down at the instrument panel (and sees all the lights on) that there is any indication that something did not go right...

greencalex

OP is moving around, but only to the extent one would expect given the changing engine rpm.


On the move OP seems strong and steady.

greencalex

Hmmm... I had not considered this, as it idles fine if it has not just stalled out.


I imagine that one never knows, however, so I'll break-out the carb cleaner this weekend...

911 Rod

What was it like before you put the clutch in?

greencalex

In the clutch lift-off that caused the stall, idle was dead steady before the lift off. There is literally no indication that anything odd has happened; no stutter, no "lurch", nothing. The stall is so silky that the only indication that it has happened is the fact that revs don't climb when you press the accelerator...


On restart (trans in N, feet off all peddles), engine immediately jumps into the oscillation.


After oscillation dies out, everything seems completely normal again.


If you then cut the engine, and restart, you don't get any oscillation on the second restart.


The low frequency of the oscillation (again, about one full cycle per second) strikes me as very strange; I would have thought that any of the control feedback loops would react a lot faster than that. This line of reasoning made me wonder of some feedback loop was perhaps not working, and leading to some sort of "limp by" mode that reacted more slowly, but as I said, I don't see any codes from the OBD2.

Aspen Autosports

I typically only see oscillation when a vacuum leak is present or the MAF isn't operating correctly.

It oscillates and then the computer corrects the mixture and makes it run smooth but something is definitely not correct.

911mhawk

I don't think anyone mentioned the boost test yet...Do one.

Even if that's not your issue, you'll know the system is tight and eliminate a common problem that causes all types of issues.
Seem many that check finds some leak that they didn't know existed, or had some intermittent problem that may have been related.

Here's something to consider:
https://rennlist.com/forums/996-turb...ak-tester.html