Ya, it sucks to diagnose a pre 96 car. In 96 domestic and imports all went to OBD 2. Prior to that they were all doing there own thing. Even My $1200 Matco scan tool will only do domestic OBD1 and of course all OBD2. I would think Volvo dealer should be able to scan it. Im not familiar with volvo but I would start with whatever type of air idle control is used. Doubt its mass air and sure its not an O2. I had a temp sensor bad on an OBD1 Infinity. It didnt idle high but ran sooo rich it smoked black and soaked the plugs in just a few miles. I wouldnt throw parts at it. Most sensors can all be checked with a multimeter. You'll just need to check that there within there operating range. Got a book for it?