Mongo

I did some more WOT bursts on the way to work and it's not doing it now. Tried the same thing last night again, and the surge/stumble didn't repeat itself at the same RPM, or any in that matter. I'll give that new crank position sensor a try before anything else.

Mongo

Ok I am facing 2 COMPLETELY SEPARATE PROBLEMS:

1) The bouncing tach and hard starting is related to the crankshaft position sensor.

2) The Surge at 4500 RPM is related to what is called the vacuum valve / changeover valve. The part number is 911 618 123 01 . I looked it up on google and found a note saying this part has supersceeded to 993 605 123 00. When I looked it up again on Rennlist here through that part number, I now get 996 605 123 01.

Per a technician at a local dealer here he indicated that when this solenoid starts to fail, a ticking sound will be noted during idle. When shutting the car off and turning the ignition on, the ticking will continue for almost 10 seconds. This unit supplies vacuum to both the heater and the tuning flap in the intake manifold. When it fails, the flappy will slam shut on occasion. Sure enough, my car is doing VERBATIM what he said.

There is a drawback to this though. The old type vacuum valve uses a Mercedes connector that is now obsolete. The connector will need to be replaced using a Fuel Injector type harness connector. Please see the images below... I guess you learn something new everyday. BTW, this connector is notorious for failling on 993's and 964's before the newer part number came out.

NEW STYLE CONNECTOR - P/N 996 605 123 01


OLD ONE FOUND ON OUR 928s - P/N 911 618 123 01

mj1pate

Be sure and prepare for extracting the old crank position sensor. There are numerous threads regarding the difficulty in extracting the old unit They tend to be stuck and break off where the harness joins the pickup. Treat the junction of the sensor and the bell housing with a penetrating oil several days before attempting to remove the old unit and don't apply any tool leverage against the old unit, during extraction.

Mongo

Got it! Will keep that in mind. My new sensor arrives today. I'm going to park it tonight and hit it with PB Blaster and let it sit till Sunday.

Lizard928

that unit does not supply power to the heater btw.

Mongo

The solenoid above? It's dedicated to the flappy only eh? Must be only for 911s then it's dedicated to that.

Lizard928

yes it is flappy only. I have yet to see one of the origonal ones bad.

Plus if it fails, it would either leak air, or not open.
It would not give the symptoms you describe.

oups59

Any picture on how it is connected?

Mongo

I'll take one when I get the chance. It won't be tonight though as I'm working late.