I really need help with a bad idle problem on our immortal 1991 745 Volvo with the Regina system and 188,000 miles. Problem: when cold, car is extremely difficult to start, will repeatedly stall, occasionally backfire; with persistent efforts it will get running but repeatedly stall until very warm; when running or driving, it lacks power. In addition to myself, two mechanics have worked on the car and between us we have either replaced or substituted with known good components each of the following parts which all remain on the car: radio suppressor relay, fuel pump relay, Regina coil, crank positioning sensor, fuel pump, fuel pressure regulator, idle air control (mounted under the manifold), checked unsuccessfully for any vacuum leaks, and last weekend we replaced with a new Bosch unit the Coolant Temperature Sensor (CTS). The timing belt and associated components were replaced about 14,000 miles ago and seem to be in good shape. The throttle positioning sensor looks okay and the throttle body itself was served by Volvo several years ago. Problem persists.
Any help from each and all would be most dearly appreciated, with a special plea to Art B and Spook!
Heartfelt appreciation, Larry