Q: engine shakes violently when car turned on

working oj thos

Hello. The vibration, bad gas mileage, and lack of power are all signs of a misfire. Your engine is essentially skipping a beat or two. This causes the combustion cycles to fall into an unusual rhythm. There are many reasons the vehicle may be facing these issues. You should have the vehicle scanned for diagnostic troubleshooting codes. Even if no check engine lights are on, the computer will still pick up faults and keep track of them. Typically caused by spark issues, a bad fuel injector can also have an effect. Both of these can be tested electronically, fuel injectors being harder to test. Look for any type of fouling on the spark plugs, and replace them if they are worn. There are also several sensors that can have an effect. The MAF sensor, IAT sensor, and several engine sensors will cause bad running conditions if they are sending bad signals to the computer. These will likely show in a vehicle scan. Do some more testing on the vehicle. Unfortunately these types of issues are a process of elimination.