Welcome Steve,
How many miles?
When did he replace the timing belt?
If not recent and it breaks the valves bend. The engine is an Interferience engine and the pistons hit the valves if the belt brakes. This is very important.
Waterpump. When was it changed? $300 or more
Power steering rack. So you see leaks? $400 or so
Has he replaced the original rubber clutch disc? Very expensive. Parts +-$800 and labor 12 to 14 hours shop time.
Shocks-how old? $400 for Boge/Sachs OEM. Koni and Bilstein $$$$
Tires? Typical $400 and up
Alignment? $100 and up
Ask about gas fumes. Typical stress crack on top center of tank. Repair $100.
Head Gasket. 1987 924S has a defect head gasket. Has it been replaced? $500 parts and labor-this we do all the time ourselves.
Shift lever- does it feel sloppy left to right? This we fix or replace $50
Now back to your original question.
It may be a simple as the balance belt off a tooth or so. Why did he replace the Balance shafts? This is NOT normal. Caution.
New engine mounts. Did he put in OEM for $350 a pair or aftermarket for $100 a pair? Some of the aftermarket do not hold up.
Idle with a good running car gets bad due to vacuum leaks-could be simple or real bad.
Do not trust your gut and get swept in. Get a professional inspection PPI at a good Porsche shop.
The 1987 has a good engine. The 1988 is a lot better. Keep looking.
Here is a link for more info
http://www.connact.com/~kgross/FAQ/944faq05.html
GL and keep posting and let us know what you find.
John_AZ
1988 924S 60K + 1987 924S 113K
1979 924 + 1977.5 924 + 1970 914 1.7 +++===gone, past tutors