frwilk@the944.com

How to become "944NA shudder-free" by FR Wilk
Fri, 1 Oct 1999

Here it is for what it's worth! For those of you with the "944na shudder",
this may make you happy. Since this is free, you get a money back guarantee
of satisfaction.

THE DISCLAIMER:

This is for information only and your not being instructed to make any
changes to your engine. You do so at your own risk. The shudder is a software
design error in the early 944 DMEs only. Early Euro DMEs do not have the problem.

THE PROBLEM:

What is the "944na shudder"? Every time you close the throttle from above
2,000RPM, the engine drops below the normal idle of 950RPM down to 600RPM
and then back to 950RPM. The engine performs a violent shudder. The
intensity of the shudder may vary and many 944na Porsche do not have the
problem.

NOT THE CAUSE:

Response cams, spark plugs, vacuum leaks, motor mounts, and auxiliary air
valves will not cause this shudder. They can cause idle problems or engine
shaking but have nothing to do with this specific problem.

THE CAUSE:

On deceleration, the overrun [coasting] fuel cut-off frequency is too close
to the idle frequency. In other word, fuel is cut-off when the throttle is
closed and does not start up again until the engine drops below 1,200RPM.
Fuel does not start up soon enough to keep the RPM from dropping below
normal idle. The overrun fuel cut-off frequency should be set higher at
1,600RPM. It is designed to save fuel. Mine dropped to about 600RPM with a
nice big shudder.

THE CURE: Revised 05/2001

For the software fix, go to 944 shudder

THE COMPROMISE:

The overrun fuel cut-off frequency is internal to the DME.  If the 
throttle-closed signal is never received, the overrun cut-off will be 
eliminated. This is a simple trick to fool the DME into ignoring the 
fuel cut -off. The software fix is beyond the capabilities of most,  
but this simple adjustment, anyone can do.

THE PROCEDURE: Revised 5/2001

Do not continue if your engine is not in good working order.  Fix it first.
With the engine off, take an 8-mm box wrench and loosen the nut on the
throttle stop screw. Operate the throttle so you hear the click. Turn out
the stop screw until the click stops. Turn the screw out about a quarter
tun past that point. Tighten the nut and lock it down. Start the engine and
turn the air bypass crew in to adjust the idle down. Set it a little high
at about 1000 RPM. What you have done is completely eliminate the
throttle-closed switch. Simple, maybe 15 minutes.

WHAT YOU GIVE UP:

There is no idle stabilizing problems. You will not know the difference 
before or after. Try it for a few weeks and you will see.

Let me know if this solves your problems. I worked hard and long to come up with this and I love to hear from people that this has helped.

F.R. Wilk   ©1999