My car is shaking at like 60 mph, only when I rest my foot on the gas and it's in gear. I tried putting it in neutral at this speed and it goes away, and while it's in neutral traveling at this speed I can bring it to whatever rpm and no shaking. Also, it shakes pretty bad when I punch it and it's in 2nd or 3rd gear, doesn't really do it in 1st. It is getting way worse recently by the way. Any ideas on what this is? I've ruled out rotors and tires and wheels being the problem so don't bother mentioning that. Has anyone ever had anything like this happen? To me it sounds like something is definitely out of balance, but what? Engine? Transmission? Torque converter? These are just guesses. Thanks.

 

I was thinking it could be the harmonic balancer, but it doesn't shake when it's not in gear, so I'm thinking not the harmonic balancer?

 

The easiest thing to try is to have the codes scanned at a parts store. Your connector is behind the ashtray. Post any codes on here.

The harmonic balancer is not a bad idea to inspect. Use white out to draw a line from the center bolt to the edge, then drive the car. If the line breaks, then the rubber is not connecting the two metal parts of the balancer.