Check the EGR valve.
my guess is the lower motor mount
Take it to A shop and have them clean the intake and throttle body housing.
Maybe you will need to clead the IACV (iddle air control valve), use a carburetor cleaner spray... Jorge,
simply put you can't if it is idleing not normal their is a problem surging/hunting idle=fuel pump/filter high idle =vacuum leak or sometimes fuel pump
1 300 rpm
cause he is stupid
I have a 1989 929, when its cold it runs real bad but once warmed up it has problems idleing, the car shakes and sometimes when stopped it stalls, mine is an auto, but when driving like on the highway it runs fine. Is your problem similar?
look for a loose vacuum line.
Probably have a misfire or lean fuel mix NELSON
Needs a recharge
check the idle control valve not that hard to replace and inexpensive