1. Basic Checks (Easy and Free):
* Fuel:
* Check the fuel level: Sounds obvious, but an empty tank will cause stalling.
* Listen for the fuel pump: Turn the key to "on" (don't start the engine) and listen near the fuel tank. You should hear a brief humming sound as the pump primes. If not, the pump might be faulty.
* Inspect the fuel filter: A clogged filter restricts fuel flow. It's a relatively inexpensive part to replace.
* Air:
* Check the air filter: A dirty air filter restricts airflow, leading to poor idling and stalling. Replace it if dirty.
* Inspect for vacuum leaks: Visually inspect all vacuum lines for cracks, holes, or loose connections. Spray a small amount of carb cleaner (or brake cleaner, use caution!) around suspected areas while the engine is running. A change in engine speed indicates a leak.
* Ignition:
* Check the battery terminals: Clean and tighten corroded terminals. A poor connection can cause intermittent starting and stalling.
* Inspect the ignition wires: Look for cracks, damage, or loose connections.
2. Intermediate Checks (Requires Tools and Some Knowledge):
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle position. A faulty TPS can cause erratic idling and stalling. A multimeter is needed to test it (check the sensor's voltage output at idle and various throttle positions).
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF can also lead to idling problems. Cleaning it (carefully, with MAF sensor cleaner) can sometimes resolve issues.
* Idle Air Control (IAC) Valve: This valve controls the amount of air entering the engine at idle. A dirty or faulty IAC valve is a common cause of idling problems. Cleaning it (with carb cleaner) might help. It can also be tested with a multimeter or by observation (does it move when the engine is started?).
* Spark Plugs and Wires: Check for worn spark plugs, incorrect gap, or cracked/damaged wires.
3. Advanced Checks (Requires Specialized Tools and Knowledge):
* Computer Diagnostics: A scan tool (OBD-I reader for this year) can read diagnostic trouble codes (DTCs) from the engine's computer. This provides valuable clues about the problem.
* Fuel Pressure Test: This requires a fuel pressure gauge to measure the fuel pressure at the fuel rail. Low pressure indicates a problem with the fuel pump, filter, or regulator.
* Vacuum Test: More advanced vacuum tests can pinpoint leaks not easily found by visual inspection.
Important Considerations:
* Year/Model Specificity: The exact location and testing procedures for components may vary slightly depending on the specific 1990 Cadillac 4.5L model. Consult a repair manual for your specific vehicle.
* Professional Help: If you're not comfortable performing these checks or if the problem persists after trying basic troubleshooting, it's best to take your Cadillac to a qualified mechanic.
By systematically checking these items, you'll greatly increase your chances of identifying the cause of your Cadillac's idling and stalling problems. Remember to always prioritize safety when working on your vehicle.
