The Regina TPS is a pretty simple device, I would have a
hard time believing it would be bad, unless it was contaminated when cleaning the throttle body or something similar.

You can check the function, and confirm that the ECU is 'seeing' the signal, buy using diagnostic control function 2 at the diagnostic unit in the engine compartment. Check the 700/900 faq for instructions, if you are not familiar.

Is it setting any codes? Have you checked fuel pressure at the rail? Have you checked the vacuum line and rubber connector ( and the electrical connector)at the MAP sensor? What kind of an idle problem is it, misfire, sputter/stumble,lope, surge etc?

The coil can also be the cause of a bad idle ( weak spark)if the internal contacts are dirty. Remove the two torx screws to separate, then clean the connectors and small metal rods.

Before you take it to the stinkin' dealer, you could go here:
http://www.volvotechinfo.com/index.cfm?event=app.home

order the FI,ignition system and wiring green books, do it yourself, and still have money left over from what they would charge.
--
Gary Gilliam Sumerduck VA, '94 940 Regina, '86 240GL