I just purchased a 1990 740 Volvo (my 1st)wagon with 216,000 miles that was not well cared for in regards to the PCV system and trottle body. Both were very dirty due to lack of care and cheap fuel. As such, I overhauled the entire ignition/fuel system, cleaned the throttle body assembly spotless, replaced the oil separator box and replaced flame trap including all related hoses. It was fully clogged and blew oil out of the oil filler cap. A real mess! I now have reasonable acceleration, gass mileage is about 19 around town, and rides well.

The odd activity with the RPM is as follows.
1. At start the RPM is as it should be; 750/800 area.
2. After about 2 minutes with no load, the RPM gradually clims up to 1600 and stays there, no hunting. Could not find any air leaks on any hoses/lines.
3. Once under load the RPM drops back to 750/800.
4. When the A/C is turned on the RPM drops and hunts around from 450 to 600.
5. When the A/C is shut off it goes back to 750/800 load and 1600 no load.

This problem has me at my wits end. Can anyone help on this?

Check your throttle position sensor for (1) continuity at both end stops and (2) proper adjustment. See the 700/900 FAQ for details.

IAC, IAC & IAC (see more info here) !

Check the temperature sensor too (not the one for the gauge but the one the ECU refers too). Is the TPS switch set correctly ?

Noel