rbuswell

1987 924S that has run well for 4-5 years. Car is stock except for a few minor upgrades. Many new OEM or better parts because prior owner deferred most maintenance _ Symptoms: 1) Engine began to run a little rough starting about a week ago but got better when warmed up. Developed a high whistle sound under the hood yesterday. Whistle didn't seem to change tone with RPM. 2) Engine suddenly shut down without warning driving at 40 MPH. 3) Wouldn't start either with no accel pedal or pushed to the floor, 4) Tried starting it again after about 40 minutes and it started so cooling off seems to matter. 5) Had it towed. 6) Started it again this morning. Let it idle for several minutes. Still ran a little rough. Didn't try to drive it so I wouldn't get stranded again. One friend suggested the DME or flywheel sensor failed. It seems like if one or the other of those failed it wouldn’t start at all, unless they can fail and recover sporadically.

Gage

Check for intake vacuum leaks.

weberlukas74

The high whistle sound could indicate a potential vacuum leak. This could lead to irregular air-fuel mixture ratios, causing rough running and potentially stalling the engine. Check all vacuum lines and hoses for any signs of wear, cracks, or disconnection. Also, inspect the intake manifold gasket for any leaks.

Plus, problems with fuel delivery or pressure can cause similar symptoms. Check your fuel pump, fuel filter, and fuel pressure regulator.

rbuswell

And now for the rest of the story:

All the fuel delivery components are close to new so that went down my list of what seemed likely. I replaced all the vacuum hoses which made no difference in performance but the old ones were brittle and cracking so it made sense to replace them. One less thing to worry about. The high whistle was in fact a worn out, busted up intake manifold gasket in the #4 cylinder. I found the leak using a nifty and inexpensive DIY tool I found on YouTube. Take a simple funnel and attach a piece of clear rubber tubing to the spout; 1/2 inch in this case. Put the funnel to your ear, start the engine and pass the end of the tube over suspect areas and listen. In less than a minute the #4 cylinder became the clear culprit. I went through the Clark's Garage checklist to replace them all. Not hard but pretty time consuming. The car quitting without warning was the DME relay. Again, Clark's Garage and a couple online mentors lead me to it. It's unnecessarily difficult to trade out in a 924S. It looked to me like the factory could have easily located the relay array in an easier place to reach. The car literally runs better than ever. It proved to me just how forgiving a Porsche is. I've owned the car for a few years and it still ran with the failing gasket. The DME relay appeared to be original on a 1987 car. The cover box looked like the old style Bakelite material. That relay is supposedly the weak link! Yet it appeared to work for 37 years.