940idle too slow

Does anyone know how i can adjust a 1994 940gl idle speed. I have set
everything to spec, including the base idle and microswitch, and the
throttle body and idle stepper motor have been cleaned, but it still idles
too slow. THe motor still drives ok and doesnt lack power or blow smoke.

It never stalls or has any hunting or unusual behaviour, and the idle will
adjust when load is placed (such as a/c) but it simply idles too SLOW. And
therefore the motor vibrates, making an otherwise pleasant car to drive seem
quite primitive. I have tried simply re adjusting the throttle spindle stop
out of spec - to make the minimum idle speed higher, but that had the effect
of making the idle speed erratic.

I have been led to beleive that the idle is not adjustable, and set by the
bosch engine controller at the factory to a very low 650 to 750 rpm. About
half the time it seems to idle ok (not as smooth as i would like but i
wouldn't be complaining now if it was like that all the time), the rest of
the time it is too slow and make everything in the car vibrate. I cant put
my finger on any particular cause (like after a long drive or idling for
too long), it just seems to drop off by about 50 rpm and vibrates.

Also, If there isnt any particular fix or reason for this problem, does any
one know of any way to trick the computer to increase the idle speed or to
activate the stepper motor just a little bit more - therefore increasing the
idle speed.

Ps. I think it is interesting that my 85 240gl with the same motor but
older (adjustable idle speed) feul injection system has an idle speed of
950rpm. It makes me think that the lower speed on the newer car is too low
& set that way for feul or emissions reduction

 

When Volvo went to the electic fan they lowered the Idle speed. check your
AC & Alternator belts, as a loose or worn belt can cause a vibration also.

Harold