1. Verify the New Parts:
* TPS: Did you get the correct TPS for your engine? A wrong part will cause major issues. Double-check the part number against your car's specifications. Ensure it's properly calibrated (some TPS sensors require this) and securely connected. A bad connection can mimic a bad sensor.
* IAC: Same as above – correct part number, secure connection. The IAC valve is sensitive to proper cleaning and seating. Did you clean the IAC passage in the throttle body before installing the new IAC?
2. Check the Installation:
* TPS: Was the TPS installed correctly? There's usually a specific idle position and a screw to adjust. Improper adjustment can lead to poor idling and running. A misaligned TPS will give incorrect readings to the computer. Consult a repair manual for the correct procedure and adjustment.
* IAC: Make sure it's fully seated and the connector is securely plugged in. A loose connection can cause erratic idling.
3. Other Potential Problems:
* Vacuum Leaks: Check all vacuum lines for cracks, leaks, or disconnections. Even a tiny leak can severely affect idle and drivability. Spray carb cleaner (or a similar non-flammable solvent) around all vacuum connections while the engine is running; a change in idle speed indicates a leak.
* Mass Airflow Sensor (MAF): The MAF sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor will cause poor running. Try cleaning it with MAF sensor cleaner (following the cleaner's instructions carefully). If cleaning doesn't help, it might need replacement.
* Fuel System: Check for fuel pressure and fuel filter condition. Low fuel pressure or a clogged filter can restrict fuel delivery, leading to rough running.
* Ignition System: Check the ignition coil, spark plug wires, and spark plugs. Worn or damaged components in the ignition system can cause misfires and poor running.
* Computer/PCM Problems: While less likely, a faulty PCM (Powertrain Control Module) could be interpreting incorrect signals from the sensors, even if they are functioning correctly. This usually requires professional diagnostics.
* Engine Mechanical Issues: A more serious problem such as a worn camshaft, lifter, or other internal engine components might be causing the poor running. This requires more advanced diagnostics.
4. Diagnostic Tools:
* OBD-II Scanner: Even though your 1993 Skylark likely doesn't have a standard OBD-II port, a more sophisticated scanner might be able to communicate with it and retrieve diagnostic trouble codes (DTCs). This will point to the most likely culprit.
* Multimeter: A multimeter can be used to test the TPS voltage and resistance to ensure it's within specifications.
Recommendation:
Start with the easy checks (vacuum leaks, MAF sensor cleaning) and thoroughly verify the TPS and IAC installation. If those don't resolve the issue, a professional mechanic with a suitable scanner will be needed to diagnose the problem accurately. Trying to fix things blindly can lead to further damage and unnecessary expense. Remember to consult a repair manual specific to your 1993 Buick Skylark for detailed procedures and specifications.
