Engine Mechanical problem
1995 Buick Riviera 6 cyl Front Wheel Drive Automatic 210,00 miles

Check engine light is on. Code comes up P1640 which gives me 3 possibilities. The torque converter locks up Ok, so that eliminates one. The other 2 are Boost Control solenoid and Evaperator canister Purge Valve. How do I determine which of these 2 is the problem? My local parts store does not carry either part. Are they dealer items and how expenseive are they?

That code is for Quad Driver Module 1. Here is a diagnostic chart, follow it and you should be able to isolate the problem. Yes, both of those are probably dealer items, but I dont have a price listing for them