964 rough running and losing power

[Brunei Boy]

I have a 1991 964 which has recently developed rough running, stalling and loss of power (kangarooing) problems. I have recently had both the distributor caps replaced but it ran OK after that. Problem really started on way to work in morning when the rpm gauge showed zero rpm with the engine running, the engine then stalled at lights and the rpm gauge was good on restart. Then a little further down the road I got all the warning lights on as well as audio beeping alarm.....so pulled over, stopped the engine and restarted with all back to normal. When parking the engine stalled numerous times. Later in the day the car was undriveable due to intermittent loss of power even with the accelerator on the floor. The car got towed!

Mechanic has identified broken down connectors for hall and crank sensors. Would the loss of hall and crank sensors give the symptoms described above? Any suggestions of possible causes would be appreciated. Also any suggestions as to where I can get replacement Hall sensor?

[GatedF355GTB]

It's highly unlikely both sensors went bad at the same time. It sounds like your mechanic may be "shotgunning" in the hopes of solving the problem. i seriously doubt your hall sensor is defective as you can actually drive the car with it unplugged (I've tried this with a 993). It could be a failing crank sensor or if your car still has a dual mass flywheel, that could also be the source of your problem.

[540964]

My first guess is ignition coils.

[Kraftday]

Sounds like the crank ref sensor. They tend to fail intermittently which can be hard to pinpoint. Not to worry, low cost fix then even if that isn't the problem, it is good to update for piece of mind, especially if renewing the flywheel / clutch.

Porsche has updated the harness plug and sender. An example:

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.com%2Fulk%2Fitm%2F22 2709572008

In some cases increasing the gap to 3mm helps clean up the signal on the upper rpm ranges too I have found.

[hienz]

Check your dual distributor belt.

[ischmitz]

The Hall sensor fails "silently". It doesn't even through a CEL because its failure is not degrading emission. But you will be slightly down on power because the ECU permanently retards the ignition by 6 degrees.

The reference sensor can do what you are describing. It can fail intermittently. The other things to look at are the O2 sensor connector and the connector to the AFM. There is a service bulletin from Porsche about placing a Zip tie onto the cable existing the AFM connector. The cable touches the firewall when the engine moves under load and that has caused running issues.

The three-pin O2 sensor connector is sometimes spotty. It makes the O2 signal momentarily drop to zero and the mixture control drives all the way to fully rich where it becomes incombustible. I had this issue and the engine would cut out under cruise conditions like "someone pulled the plug", Then all of a sudden it would kick in again.

A simple test is to unplug and re-plug it a couple of times. This cleans the contacts. In my case it gets things back to normal for about 6 month.

[RedCoupe]

My 964 had similar stalling/poor running/not starting issues that persisted through all sorts of diagnostic work until we discovered that the negative battery cable had measurable resistance, terminal to terminal. A new battery cable solved all of the problems.

[mikedsilva]

All of the above can be true... in my recent experience I had the same issue as you describe.

Here is a video of what I saw on my dash... it did in fact turn out to be a dodgy coil.
https://www.youtube.com/watch?v=gLLs8-nwhpI