The early Porsche 944 (1982 to 1985.5)
has a pronounced engine shudder. On engine deceleration, the engine will drop several
hundred rpm below normal idle before returning to normal. The whole car shakes. This
shudder problem seems to affect the US version of the early 944 more than others.
Technical Description: On engine
deceleration, the throttle switch is closed and the fuel is cut-off. This is a design
feature. As the engine speed drops below 1,600rpm, the fuel begins to flow again. The
engine then returns to a normal idle. This is how it is suppose to work. But.........
The early Porsche 944 engine computer (US DME) has a fuel cut-off set at 1,350rpm.
The fuel flow start too late. My engine dropped to 600rpms before returning
to normal idle of 950rpm. The shudder was very pronounced. The worst part of this is the
shudder could not be fixed. It was internal to the fuel injection computer and swapping
DMEs gets you another computer with the same problem. The early Porsche 944 Euro version
has a fuel cut-off set at 1,600rpm and does not have a noticeable shudder problem unlike
the US version.
Update 2002: There is now a bug fixed
version of the 944 DME operating code. I have modified the code to increase the fuel
cut-off point to 2,000rpm. The code has been thoroughly tested and the shudder is gone!
NOTE: Not all early US Porsche 944 show
symptoms of the shudder or it is so mild as not to be noticed.