Q: Car Vibrating and bottoming out

The basic condition of the engine can be verified through a cylinder compression test. If the compression in each cylinder is within factory spec., there is not too much variance across cylinders, and you are not using more than a quart of oil every 2,500 miles, then your engine is perfectly good and you simply need to have the fuel, ignition, air induction, or sensor fault pinpointed. Although the underlying actual cause of the misoperation should be pinpointed, in your case, with the high mileage and the particular symptoms, you’d probably benefit by removing all the fuel injectors from the fuel rail and send them out for restoration (Mr. Injector, etc.). Each one of the fuel injectors has a tiny filter basket and the injectors have incredibly small passages. When they get plugged up, engine performance degrades considerably and this is a very common circumstance. If you request a diagnostic to pinpoint the cause of the rough operation, among the items that will be considered are the engine coolant temperature sensor which must be working properly to signal the PCM to enrich the mixture on cold start, fuel delivery problems, vacuum leaks (including EGR), an air induction fault like a stuck idle air control valve or a faulty throttle position sensor, problems with the mass air flow sensor, defective spark plugs, a weak coil and defective oxygen sensor(s). If you desire that this problem be diagnosed by a certified Mechanic, dispatched by YourMechanic right to your location, please request a rough idle diagnostic and the responding certified mechanic will get this resolved for you. If you have further questions or concerns, do not hesitate to re-contact YourMechanic as we are always here to help you.