Ignition System:
* Worn spark plugs or wires: This is a common and relatively inexpensive first check. Worn plugs misfire, causing the engine to shake. Cracked or worn wires can lead to the same issue.
* Distributor cap and rotor: These components distribute the spark to the plugs. Cracks, corrosion, or wear can disrupt the spark delivery and cause a rough idle and shaking.
* Ignition coil: The coil supplies high voltage to the distributor. A failing coil can produce weak or inconsistent sparks.
* Ignition module (or control module): This electronic component controls the ignition timing. A faulty module can cause erratic ignition timing, resulting in shaking.
Fuel System:
* Dirty fuel injectors: Clogged injectors deliver an uneven fuel spray, leading to a rough idle and shaking. Cleaning or replacing them might be necessary.
* Vacuum leaks: Leaks in vacuum hoses can disrupt the air/fuel mixture, causing an erratic idle and shaking. Inspect all vacuum lines for cracks or disconnections.
* Fuel pressure regulator: This regulates fuel pressure to the injectors. A faulty regulator can deliver incorrect fuel pressure, leading to a rough idle.
* Dirty air filter: A severely clogged air filter restricts airflow, disrupting the air/fuel mixture and causing rough running.
Engine Mechanical Issues:
* Worn engine mounts: These mounts isolate the engine from the chassis. If worn, they allow excessive vibration to transfer to the car's body, making it feel like the engine is shaking more than it actually is.
* Balance shaft: The Tempo might have balance shafts to reduce vibrations. Problems with these shafts can lead to noticeable shaking. This is less common but a possibility.
* Low compression in one or more cylinders: A cylinder with low compression will not contribute properly to the engine's power stroke, causing unevenness and shaking. A compression test is needed to diagnose this.
* Valve train issues: Worn or improperly adjusted valves can contribute to rough running.
Troubleshooting Steps:
1. Start with the easy checks: Inspect the air filter, spark plugs and wires, distributor cap and rotor for visible signs of wear or damage.
2. Listen carefully: A distinct misfire can sometimes be identified by listening to the engine, which can narrow down the likely culprit.
3. Check for vacuum leaks: Spray a carb cleaner (or similar) around vacuum hoses while the engine is idling. A change in engine speed indicates a leak at that point.
4. Obtain diagnostic codes: If the car has an OBD-I system (unlikely on a '91 Tempo, but possible depending on trim and options), a scan tool can retrieve diagnostic trouble codes (DTCs) to pinpoint potential problems.
It's important to systematically check these areas. If you're not comfortable working on your car yourself, take it to a mechanic for diagnosis and repair. Ignoring a shaking engine can lead to more serious damage.
