Q: car vibrates badly at 40+ but only when gas is being applied

Hello, thank you for writing in. Vibration and shaking is typically associated with a poor combustion taking place inside of the cylinders. This can be spark, air, or fuel driven. Think of it this way, the vehicle has a constant supply of spark and fuel, what the computer controls with the throttle is the air intake. When you take your foot off of the accelerator, there is a valve that is used to steadily drop the air intake to the engine rather than just cutting it off and stalling the engine. This is the idle air control valve, and it may be failing. You may also want to test your spark system and fuel pressure if the issue is not related to this valve. Only further testing will tell.