* Vacuum Leaks: A vacuum leak can disrupt the air/fuel mixture, leading to misfires, especially at idle when vacuum is highest. The increased RPM (and thus increased engine speed and manifold pressure) temporarily compensates for the leak. Check all vacuum hoses for cracks, splits, or loose connections, paying close attention to the brake booster hose.
* Idle Air Control (IAC) Valve: This valve regulates airflow at idle. A dirty, sticky, or failing IAC valve can prevent the engine from maintaining a smooth idle, causing misfires, especially under load (like going uphill). The increased RPM bypasses the IAC's control to some extent.
* Throttle Position Sensor (TPS): A faulty TPS provides inaccurate information about throttle position to the engine control unit (ECU), leading to incorrect fuel mixture calculations. This is more likely to cause problems at idle and low RPM.
* Mass Airflow Sensor (MAF) Sensor: This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor will provide incorrect readings leading to an improper air/fuel mixture. This, too, is more pronounced at low RPM.
* Spark Plugs and Wires: Worn or fouled spark plugs or damaged ignition wires can cause misfires. This is a possibility, but less likely given the RPM-dependent nature of the problem.
* Fuel injectors: A clogged or malfunctioning fuel injector can cause a lean condition leading to misfires.
* PCV Valve: A clogged Positive Crankcase Ventilation (PCV) valve can increase crankcase pressure and disrupt engine operation, potentially causing misfires.
Troubleshooting Steps:
1. Check for Vacuum Leaks: Visually inspect all vacuum hoses. You can also use a vacuum gauge to check for leaks in the system.
2. Clean the IAC Valve: This is a relatively easy DIY repair. Remove the valve, clean it with carburetor cleaner, and reinstall it.
3. Check the TPS and MAF Sensor: These usually require a multimeter to test their output voltage against specifications. You may need a repair manual to find the correct test points and voltage ranges.
4. Inspect Spark Plugs and Wires: Check for wear, fouling, cracks, or damage.
5. Check Fuel Injectors: You'll likely need a fuel pressure gauge for this step.
6. Check PCV valve: Inspect for clogging.
Important Note: If you're not comfortable performing these checks yourself, take your Cadillac to a qualified mechanic. Ignoring a misfire can lead to further engine damage. The fact that it's related to hills and low RPMs suggests a relatively serious issue that needs professional attention if you're not experienced with auto repair.
