I have a 1988 740 turbo. Perhaps someone can help with trouble shooting a rough idle. So far I have:
-checked for vacuum leaks. No problem
-Cleaned throttle body. All ok
-Checked timing, base idle, wires plugs etc. All OK
-Pulled idle control motor, cleaned and tested off the car. Works fine

Now here comes the electrical testing. I pulled the connector off the ECU to do the tests shown in the Volvo green guide. All OK except:
-At pin 12 on the connector(the CIS grounding wire and wire through the fuel injection relay to the injection control computer) there is some resistance. According to the book the reading should be infinity.
-At pins 10 and 23 (the idle air control ground sides) when connected to 12 volts gave a resistance of infinity. It should be about 20 ohms.

This leads me to believe the fuel injection control computer is faulty. A mighty expensive part so before I buy..........does this seem reasonable. What else can I do to check it out. Thanks for all input.

Trade you ECU out with a junkyard, or known working one and see if it solves your problem. Or, if you get the part num. off of the computer someone here on the site may have a spare.