Waldteufel

My 97 C4S has had a problem since new whereby the engine will sometimes stall when either the clutch is depressed or at times even when just backing completely off the accelerator. It seems to act like it has a LWF, but it doesn't....or at least I didn't order it that way. None of the mechanics I've polled has a clue what might be causing this, but the momentum from the dropping RPMs dip below the stalling threshold before the ECU has time to compensate. Normally, the RPMs will drop to about 550 RPM (idle on this car about 750 RPM according to the tach) and then bounce back up to about 900 or so once the DME compensates before settling back to idle. It occurs both when cold and even after hours on the interstate, at which times I can depress the clutch as I enter an offramp and the engine will stall before I have time to downshift.

The car is a 97 so it shouldn't have the dual processor DME as on the 96 models, but I'm wondering if I somehow got a 96 DME on a 97 as the car was built in September 96? Other possibilities I'm mulling over are a faulty/dirty flywheel timing sensor; or even a DME that's set for a tiptronic on my 6-spd manual.

I've thought of going to an aftermarket chip, but don't want to be chasing my tail on this. Might some sort of commercial remapping work? I know it's normal that it will stall a few times whenever the battery is disconnected (until it adapts to its new idle), and I've tried turning on several power consumers (fans etc) during this adaptation process, but to no avail.

Any ideas would be greatly appreciated. Thanks, Tom

k722070

search 'ISV' in the 993 forum and get that checked off the list before spending any money on a chip.

Waldteufel

Had the ISV replaced early on in the process. That was the first recommendation of the mechanic at the dealership, but it had no effect. The idle is normally not unstable; the RPMs just dip too low before the DME can intervene.

Spidey 993

I swear i was reading a thread on a 993 owner having stalling issues on the downshift especially, purchased the Wong chip and resolved the issue. I ran into the thread because i am considering the chip, but i don't have this problem. I'll keep looking for it and send to you if I find it, but SEARCH is your friend on this one.

There was some discussion on the thread that Wong would increase the idle just enough to ensure to resolve the problem. Some guys were saying he doesn't do this by default, but you can request it. Keep searching....

Spidey 993

Here it is: it is a 95 with LWF but sounds like something worth reading given your issue.

https://rennlist.com/forums/993-foru...lutch-lwf.html

Stealth 993

Sounds like you might have a intake leak. Has the shop checked to see if there are any stored codes? Have you done any logging of the O2's to make sure your not running lean? Also make sure the TPS is hitting idle.

You might also want to clean the MAF.