Volvo Repair: Erratic idle, coolant temperature sensor, flash flash flash

Question
I have a 1990 Volvo 740 turbo with 205,000 miles. The car is running with an erratic idle, when the car is in park the tachometer cycles between 1000 and 2000 rpms.  I checked for loose or disconnected vacuum hoses and did not find any.  When the car is in drive the idle is lower but the car shakes.

Answer
there are many things that can cause this it could be a bad idle speed motor,engine coolant temperature sensor,air mass meter,throttle switch.you could try checking for any diagnostic trouble codes.


n the engine bay on the drivers side near the strut tower there is a small black box with a wire attached to it.place the wire in the terminal marked 2.turn ignition key on (not started)press the small button for 1 second and the code will be displayed as a series of flashes.a red led displays the codes.the code will be three digits.small pause in between flashes for a single number long pause between flashes for the next number.example 121 will be flash.....flash..flash.....flash.repeat three times or until first code repeats itself.to erase the code after all codes have been checked hold the button for a good 5 seconds then release the light should light steady,then press for another 5seconds.this will erase the codes.  email me the codes and i will tell you what they are..socket 2is the fuel system 6 is ignition.