Hello:

My high school age son and I just went through a 1990 240 wagon (220K miles) top to bottom, and then took it on a 500 mile trip. It ran fine, except for an annoying metallic rattle that only occurs on light acceleration, never coasting/decelerating, and not when hard accelerating. I have the transmission cooler lines buffered with old pieces of hose, then zip-tied together, and I doubt it was that. I am thinking exhaust system or maybe steering pump belt? The car is in immaculate condition, and I just don't know what else to suspect. Thanks.

Greg

 

its probably exhaust shields, like the one on the cat is quite prone to that.

the belts tend to squeal rather than rattle.

 

I have also had issues with the heat shield on the exhaust manifold rattling. I finally got annoyed enough that I removed it entirely as it is only there for the pre-heater hose.

 

Or it could be the cat internally falling apart and rattling... But I'd look at the shields first as they are much easier...