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Old 06-21-2016, 08:16 AM   #1
Santa Barbara, CA
Join Date: Mar 2016
Posts: 38
Momentary Hesitation @ 4000 rpm & TC issue. Is it the DME or ???

Re: 986 1998 2.5L 5sp MT 139k 5.2.2 DME.

Engine cutout issue: When I accelerate aggressively the engine cuts out momentarily at around 4000 rpm. The CEL flashes on and off once but leaves no codes. This happens maybe 25% of the time, other times, the car runs very well without a hiccup.

TC issue: Coincidentally, after starting up, and at idle, the TC light and switch work normally, but as the car gets up to speed, e.g. 30mph, the TC light comes on and the button won't cancel it. The SB P-Dealer said the wheel speed sensors checked out okay (see below)

Since I got the car in March in need of several repairs, I have replaced the Bank 2 Solenoid, ramp and timing chain, all spark plugs (Bosch) Beru coils, Bosch MAF sensor, cleaned the Throttle body, new starter, battery, oil cap, fuel cap & fuel filter. Compression in cylinders is 165-180 psi. Fuel pressure is 48-55 psi at the rail.

I took it to the SB Porsche dealer for diagnosis of these two issues. Without another 4 hours of diagnosis, they were not able to nail the problems down, but gave me the following report.

"Scanned car found codes 5284 and 5285 in TC and fault 108 in DME. TC codes are for no comm with DME, wires from DME to TC tested okay. Disconnected TC and found car ran the same. When car cuts out CEL lights but no codes. This is indication of DME losing comm or power. Need further testing to determine cause."

I'm thinking my next step is to send the DME to be tested.

Any suggestions on other tests or how to proceed greatly appreciated.

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Old 07-01-2016, 02:40 AM   #2
Santa Barbara, CA
Join Date: Mar 2016
Posts: 38
Update: it's a vacuum leak

After unfruitful trips to a local indie German shop and the Santa Barbara P-dealer, I followed a suggestion from "itsnotanova" to check for vacuum leaks. I found one (using starting fluid method) in the top breather hose connection with the AOS and fixed it. Now the car runs without the hesitation under acceleration. Still trying to sort out the TC light issue, but the car is running great. Thanks again, to Woody for his research and suggestion.
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Old 07-01-2016, 04:24 AM   #3
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Join Date: Jun 2014
Location: LB, Germany
Posts: 1,370

just for my better understanding. TC light means traction control light. Right?

Did they check the error codes whlie driving or only when car stands in the workshop?

What wheel and tyre dimension are you driving on your car? Anything unusal or stock?

Thanks & regards
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Old 07-01-2016, 06:52 AM   #4
Santa Barbara, CA
Join Date: Mar 2016
Posts: 38
Yes, sorry, TC is traction control. The light comes on and stays on after the car starts to move.

Stock 17" twist wheels and tire sizes. Recent 4 wheel alignment. New rotors & pads.

Not sure if they checked it moving, but the SB dealer said all 4 wheel speed sensors checked out okay.

I have just received a durametric enthusiast but am not sure if the cryptic ABS items have any effect on TC.

Any suggestions very welcome and appreciated.

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