It's not an issue of the shop not being able to fix it. The issue is that the shop has trouble duplicating the problem, and I can't have my car in the shop for months at a time.

my 83 944 had the EXACT same problem and it was the ignition switch; forget you wiggle test, it only works when it is first going out. common knowledge: heavy keychains cause ignition switch to wear out early and weird on these cars, this is actually a common problem

UPDATE: A guy from rennlist was nice enough to lend me 2 DME's to test out. I drove my car for 30 minutes this morning, parking it at 10am in partial shade. I went out to start it at 7:15pm, over 9 hours later, and it would not start. This was with one of the borrowed DME's in place. I tried swapping in the other DME. Nothing. I put in my spare DME relay. Nothing. The inside of the car was pretty hot from sitting in the sun all day. I've begun to notice that my problems happen with greater frequency in heat, when the car is warm. The engine had certainly cooled off from the drive 9 hours earlier, but the interior of the car was hot and the exterior felt like it had been warmed a bit by the sun.

Another dead end.

Has the coil ever been changed on your car?

it has.

Did you replace it with an OEM coil? If not most coils do not come with a ballast resistor and the OEM coil for the 944 does. And from what I read if it does not have a resistor it can do damage to the coil or DME.

Here is a good thread that brings this to light.
http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/354156-944-turbo-msd-ballast-resitr.html

hmm...coil was replaced before I bought the car, but the PO included a spare coil with the car. I believe they are both OEM.

I've replaced or tested with new parts:

ignition wires
dist. cap, rotor
DME relay
DME
removed aftermarket alarm
fuel pressure regulator


I am at a loss. Everything that's been suggested to me has come up a dead end. I was sure this DME thing was going to be it, based on what I've read. I am so frustrated.

Pete, have you tested the speed and reference sensors? I am starting to think there is a very good chance this is your culprit. There is good documentation on Clark's Garage http://www.clarks-garage.com/ on how to do this (IGN-02 Speed and Reference Sensors - Checking, Replacement and Adjustment). If you need help doing this, shoot me a PM. It would not take us long at all to check out.
- Nate

Introduction
Bad ignition switches are becoming a more common cause of starting problems on 944s. So, take a look at your ignition switch and if it's cracked, it's likely the source of your problem This procedure is used for testing purposes to determine the condition of the cranking portion of the ignition switch and the wiring from the ignition switch to the starter.

Tools

Wire jumpers
Multimeter
Testing Procedure


Disconnect the battery positive lead.
Disconnect the electrical plug from the ignition switch.
Check the operation of the cranking contacts on the ignition switch as follows:
Connect an ohmmeter between Terminals 30 and 50 on the ignition switch. If you are unsure which terminals those are, look at the electrical connector for the wires that attach to the ignition switch. If the wires were still connected to the ignition switch, Terminal 30 would be connected to the large diameter Red Wire and Terminal 50 would be connected to the large diameter Red Wire with Black Stripe.
Turn the ignition switch to the start position as if cranking the engine and read the resistance.
The resistance should go from and infinite resistance to approximately 0 ohms when the switch is turned.
If the correct resistance is not obtained the ignition switch is bad and should be replaced.
If the ignition switch checks okay, check the ignition wiring as follows:
Disconnect the wire from the switch terminal on the starter solenoid (bendix).
Make up a jumper to reach from the starter to the ignition switch.
Attach the jumper from the switch lead at the starter solenoid (Red Wire/Black Stripe) to the Terminal on the ignition switch electrical connector with the Red Wire/Black Stripe.
Check the wire resistance with and ohmmeter. It should be approximately 0 ohms (less than 5 ohms). If not, the wire is broken and should be replaced.
Clark's Garage © 1998


i got this from clarks could be something as simple as this,it's worth a shot if nothing else has worked. good luck.