Jeff,
3 things that you haven't checked that could cause your problem, (or at least not mentioned to have been checked) the most common cause is a dirty throttle body (especially on a turbo car), which is best cleaned by removing the t/b. you can get it 90%clean on the car with an old toothbrush, a rag and carb cleaner. rmove the intake tube,clean the plate and the bore. Depending on the emmision system there will be two different throttle position swensors. (TPS) one system has a potentimeter and is not adjustable the other will have slotted mounting holes and reads idle, off idle & wot if you have the slotted TPS listen for a click when opening the throttle off its rest and back. check the faq section I believe there is more info on checking TPS there. I've found a couple of cars that have had connection issues at the coolant temp sensor(CTS) that also cause erratic idle problems. the CTS is under the intake manifold toward the rear the front sensor is for your dash gauge. also see the FAQ section for more info. will be at my friends repair facility tommorow. will try to get correct wire harness info if you dont find it in the FAQ,s
Bentwrench

79 242/72 144s/87 740/93 940
part time Troubleshooter for Volvo specialist in Rennsalear NY/ Full time md/hd diesel-gas tech for large corp w/ lots of brown trucks. may take a day or 2 to get another free minute