Saab: RPM fluctuates after warming up., vacuum leak, clutch disc

Question
QUESTION: I have just acquired a 11/1988 900i 5spd manual sedan which has done 248000km, non-turbo, and after it warms up, the idle rpm starts to fluctuate. Also when moving off in first or reverse it needs extra rpm to prevent 'shuddering'. Any clues as to what to check?

ANSWER: Rick:  Sounds like the automatic idle control (AIC) valve or a vacuum leak. The valve usually fails due to carbon buildup within, and can often be restored by generously spraying with carburetor cleaner.
  The same cleaner can be used to pinpoint a vacuum leak by spraying it in the vicinity of any suspected area while the engine is running and noting if the engine momentarily speeds up due to temporary enrichment; if so, that is the site of the leak.

 Hope this helps,
         Jerry

---------- FOLLOW-UP ----------

QUESTION: Thanks for your reply, it verified what I did to fix half my problem. I solved the fluctuating rpm problem prior to your reply by repairing two perished vacuum hose fitments (new pieces of hose), now it sits at its correct idle range. My other problem now only lies with the shudder if the rpm is kept below 1800 while proceeding to reverse. High rpm eliminates the shudder. I tried putting the brake on and slowly letting the clutch out in 1st and reverse to check to see if there was any engine movement but the movement to me seemed very minimal.

Answer
Rick:
 The shudder could be caused by a contaminated or warped clutch disc....
 Can you determine if:  The shudder is caused by a distinct lack of engine power OR a mechanical issue such as motor mounts (to which you alluded) or the clutch issue?

 If the former, then consider a weak fuel injector (low probability) due to satisfactory idle. In decreasing likelihood, consider sensors, fuel pump pressure, etc.
 If the latter, then the clutch is the likely culprit.
         Jerry