Tachometer swan dives; 88 Volvo 740 Turbo

[JungleAcid]

After I press in the clutch and let off the gas, as in when I approach
a stop sign or shift, my tach will plummet to the first notch above
zero (less than 500 rpms) and then climb back to 1000 and idle
steadily. If this gets worse I will be stalling out, obviously. What
is going on and what can I do to repair it?

James Moening
jazzkind(at)fast.net

 

[James Sweet]

Clean the throttle body and check the adjustment of the throttle plate.

 

[Rob Guenther]

Is this the same on every car? My friends Mazda (1993 MX-3 Mystere) does the
exact same thing, he hasn't had any driving related problems from it tho.