* Spark Plugs and Wires: Worn or damaged spark plugs and/or ignition wires are a very common cause of misfires (the "missing" feeling) and subsequent shaking. These are relatively inexpensive and easy to replace.
* Distributor Cap and Rotor (if applicable): Your Thunderbird might have a distributor (less likely on a '93, but possible). Cracks or corrosion in the cap or rotor can interrupt the spark, causing misfires.
* Ignition Coil(s): A failing ignition coil (or coils, depending on the engine) can't provide enough spark to ignite the fuel-air mixture consistently, leading to misfires and shaking.
* Fuel System Issues: Problems with the fuel injectors, fuel filter, or fuel pump can cause a lean fuel mixture, leading to rough running and shaking. A clogged fuel filter is a relatively easy check.
* Mass Airflow Sensor (MAF): A faulty MAF sensor provides inaccurate readings to the engine computer, resulting in improper fuel delivery and potentially causing misfires.
* Engine Mounts: Worn engine mounts can allow the engine to vibrate excessively, leading to a shaking sensation, even if there aren't any misfires.
* Balance Shaft (if applicable): Some engines have balance shafts that help smooth out vibrations. If a balance shaft is failing, it can create more vibration.
* Transmission Problems: While less likely to cause a "missing" feeling, transmission issues can sometimes manifest as shaking.
What you should do:
1. Check the basics: Start with the easiest and cheapest checks: Inspect the spark plugs and wires for visible damage. If you're comfortable, you can try replacing them.
2. Get a diagnostic scan: Take your Thunderbird to an auto parts store (like AutoZone, Advance Auto Parts, etc.) and ask them to perform a free OBD-II scan. This can often pinpoint the source of the problem by reading diagnostic trouble codes (DTCs).
3. Consult a mechanic: If the OBD-II scan doesn't reveal the problem or if you're uncomfortable performing basic maintenance, take your car to a qualified mechanic for diagnosis and repair. They have the tools and expertise to pinpoint the issue accurately.
Don't continue driving the car extensively with a significant shake, as it could cause further damage. The sooner you get it diagnosed, the better.
