993tt mystery engine events - advice appreciated

[foxj0001]

Hello,

I've recently acquired a 1996 993tt which is beautiful to look at and great fun to drive (I posted recent pix). All is well except for the following mysterious engine symptoms:

Event consists of the throttle pedal "going soft", accompanied by momentary loss of power and CEL transiently illuminates. All these simultaneous, the event is over in less than a second, CEL goes off, throttle response and power come right back. Happens when fully warmed up (or at least has not yet happened when cold). Happens up to 3 or 4 times within a 5min period. Happens whether driving hard, accelerating, or driving "family style". Even happened twice this morning at idle, as I was letting the engine cool down after driving to work. No backfire and seems like it is not misfiring, certainly not running rough. No smoke. Oil recently changed, has always had Mobil1. Using 93 octane pump gas, and I do not let the tank run too low before filling up.

Prior owner had ECU reprogrammed through Fabspeed, who also installed custom, "stock-like" mufflers (very quiet) which I had them take off and replace w muffler bypasses (not quiet!).

I had it to the dealer where I bought her to look into this and they told me that because she was chipped she was not storing any CEL-related codes, and they could not reproduce the symptoms.

So here I am, mystery unsolved. MAF sensor dirty? Distributor problem? ECU hiccup? Any ideas?

Thanks for thinking about it.

Jonathan

[DJbrand1]

Hmm, not too familiar with the 993tt motor, but I would start with reference sensors. I assume that motor has a throttle position sensor. You may to make sure they are working properly.

[bobt993]

When you say soft pedal are you saying loss of power?  You may want to invest in an "unchipped computer"  so you can pick up the fault codes.  Engine knock sensors, MAS airflow sensor, bad TPS sensor, flywheel sensor could cause issues.  You could also have a harness issue or a bad ground.  Look through the service history records provided with the car.

[foxj0001]

Thanks for replies. You may wish to look at the replies I have received on Rennlist in the 993 turbo forum, interesting and possibly informative.
I have investigated the availability of a stock ECU.
Not readily available used, when an engine is salvaged from a wreck the ECU is salvaged along with the block and recycled as a unit.
A new one is $4500 (ouch).
The adventure continues!
Jonathan

[bobt993]

You should be able to get a loaner and the associated immobilizer/key fob to pull codes using a hammer.  Any of the mentioned above can cause erratic power, stalling and sloppy throttle.  Moisture in the computer can cause this also if there was water in the back seat area at any time.  The ECU has a poorly designed back plane with a plastic insulator that if it gets any moisture causes erratic operation.  Your chasing a big loop of related parts and without fault codes it is a bit difficult figure out.  The NA 993 had harness issues that were a factory recall.  I am not sure if this affected the TT.

[size="3"]"10,300 U.S. and 455 Canadian 911 Carrera and 911 Carrera 4 vehicles [that] fall within the scope of this campaign.  Also, a total of 779 U.S. and 65 Canadian 911 Turbo vehicles are affected"[/size]

Have the VIN checked on your car for this issue and if the repair was done.  Harness is easy to change on a 993.

[foxj0001]

Thanks for reply. Dealer checked and my car was not within scope for the harness recall. Working on other leads.
Jonathan

[foxj0001]

Hello, an update.
Sent ECU back thru speed shop to tuner who determined that there was a faulty connection between motherboard and daughter board, replaced socket and daughter board under warranty and 150mi later no blips only smiles. Will come back with additional followup as appropriate, hopefully this is case closed.
Jonathan

[ccm911]

Don't you wish they all ended this way?