Porsche Repair: violent shudder from engine, porsche engineers, balance shaft

Question
My question concers a 1988 Porsche 944 - non turbo 5 speed.  When I rev the engine - out of gear - there is a vibration from the engine or transmission when the engine is slowing down to it's normal idle speed.  I can't detect a broken motor mount or any other visible cause.  Could this be a damaged pressure plate or worn bearing? The car drives ok otherwise. I want to buy the car but I would like to have an idea to work with to locate this shudder.  Thanks

Answer
Frank, very smart of you to try to understand this issue BEFORE you buy.  As to what it could be, I won't list ALL the things in your car that go round and round when the engine is running...let's just say the list is long and distinguished.  Frankly, they are all suspects.  Here's three very different ideas:

1.  This "feature" was supposed to be corrected earlier than '88.   I'm not sure if it applies to your car, but there was a program in the older computers that actually shut off the fuel supply on deceleration (to save fuel and to meet emission laws).   The computer let the fuel return at some preset rpm level.  The idea was that this could be done "smoothly", but it's something I'd consider.  See if you can notice the engine "restarting" at some close to idle speed , like 1300, or in that range.

2.  The clutch is a very obvious place to look.  If the car is OK otherwise and you don't locate the shudder elsewhere, I'd just factor in the cost of a clutch job, unless the owner can show it's fairly new.

3.  I always suspect the balance shaft and camshaft belts on these cars, just because I've always been mystified by this design.  I have great respect for Porsche engineers, except when it comes to having rubberized belts deep inside the engine where oil and heat and very bad for rubber stuff is likely to be.  I suppose the questios you need to have answered is when were the belts last replaced, when were they last adjusted, who did the work, and depending on the car's mileage, what's the likelyhood that the belt sprockets and guides are worn?  So how do you know for sure?  See below:

The condition of the car is a function of how often... and the quailty of... preventive maintenance.  To be honest, the average 944 owner doesn't always see the 944 as the "investment" most 911 owners see their cars.  Consequently, they fix things as they break, not before.

I'd gauge my feelings about this car on whether the owner can show documentation of the care associated with a true concern for preventative maintenance.  

Dave