The car (lancer evolution X) was in my garage for almost a year. I had just changed my gear box (SST) serviced it and changed my tires. Everytime I turn on the car the entire thing vibrates violently with some knocking and even worse when at high acceleration/speed 75mph. However, there are times when I push the car drive fast or it all goes away for that entire day and the car feels as good as new. The next day the same thing happens. I found some oil stains on the engine and gearbox but engine and gearbox oil level are fine. There is barely any power loss gear shift is good no engine signs at all. No smokes from the exhaust and the oil cover is clean. Coolant liquid is thick green though as apposed to clear green? Coolant level and signs are also fine.
My car has 58000 miles.
My car has an automatic transmission.
This seems to be a torque converter issue. The bolts are probably loose between the converter and the flex plate. To get to the torque converter bolts, you will need to remove the starter from the engine and then you can access the converter bolts. Sometimes the flex plate could be cracked, making the same sounds and vibrations. The other thing that could cause an engine vibration that goes away at times is a loose heat shield on the exhaust system. Check the heat shield for any looseness and tighten it if necessary. If you need assistance, seek out a professional, such as one from YourMechanic, who can help you track down the source of the vibration in your vehicle.