I'll start at the beginning. The car is a '92 245 M47. It's always had plenty of power and delivers 29 mpg, but will consistently backfire when I lift the throttle, i.e. shifting or coasting. It doesn't happen every time, but it does often enough, warm or cold makes no difference. I picked up a good description of the sound not too long ago on the board, "like someone tapping on the inside of a can."

Plugs, wires, cap and rotor, and coil are good. O2 sensor is good. The TPS shows proper voltage closed and open. Is there any such thing as a "lazy" TPS, proper voltage but too much time to reach it?

As it happens, I was buying some junker sway bar links from a local indy Volvo dealer/mechanic/salvage yard and described this problem to the owner. He told me that even though the manuals say timing is not adjustable, the distributor can wear out its adjustment after 13 years, 195K. He then pointed out that there is an adjustment bolt on the distributor and I could try rotating it just a little "by feel" to see if that clears up the backfire. According to the Volvo guy the red blocks aren't all that picky about timing when it comes to delivering power and mileage, so most people never notice if the timing goes out a few degrees.

I'd really like some more opinions on this one.

Thanks for your help.
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Jim - '92 Red 245 195K, and sometimes an '85 245 275K+