1987 240 rattles when hard accelerating

Hi all,

New member here. I just picked up a Volvo 240 automatic and loving it. Slowly fixing little things here and there. Did the front seals, timing belt, flame trap, new muffler. Next on the list is the rear trailing arm bushings and brakes.

One thing I am having a question on it the car runs great but when I try to hit the accelerator hard, I hear a little rattle coming from the engine. It almost sounds like a valve fluttering perhaps from the throttle body. Is this common in older cars? And is this normal?

Thanks in advance.
Ken

check the motor mounts

Thanks philski. I have a feeling it is something different than the motor mounts. Almost sounds like a butterfly valve fluttering and clicking on the side of a wall. I used to have the same sound on my first car which was an old Buick Century.

Check the base timing is set correctly.

Piston slap or too low octane gas.

sounds like its detonating? Is your pre-heat thermostat stuck open?

Thanks for the leads. I'll fuel up with high octane gas next time I get gas and see if it stops.

Blkaplan: Can you elaborate on the pre-heat thermostat? What is happening when it gets stuck open?

There is hose that goes from the exhaust manifold to the air inlet box... on the airbox there's a thermostat that keeps that door shut unless the car is cold. if it fails open you will be sucking hot air from the exhaust manifold. that can cause the car to detonate (rattle)