1. Check the Obvious (Easy Fixes First):
* Choke (if equipped): While less common on 1993 cars, some might still have a manual choke. Ensure it's fully disengaged.
* Vacuum Leaks: Carefully inspect all vacuum lines connected to the intake manifold, throttle body, and related components. Look for cracks, loose connections, or collapsed hoses. A small leak can significantly affect idle. Spray a little carb cleaner (or starting fluid, carefully!) around suspect connections while the engine is running. A sudden change in RPM indicates a leak at that point. Repair or replace any faulty hoses.
* Throttle Plate Sticking: With the engine OFF, manually open and close the throttle plate (the butterfly valve in the throttle body). It should move freely. If it's sticky, try cleaning it with throttle body cleaner (following the instructions carefully). Be aware that some throttle bodies require special tools for thorough cleaning.
2. Focus on the Likely Culprits (More Involved):
* Idle Air Control (IAC) Valve: This valve regulates the amount of air entering the engine at idle. A faulty IAC can cause a high idle. You might be able to try cleaning it with electrical contact cleaner (the type suitable for electronics). Locate the IAC valve (usually on the throttle body), disconnect it, and carefully clean any debris. Reconnect it and see if the idle improves. If cleaning doesn't work, replacement is likely necessary. This is a relatively easy part to replace, but you'll need to find a replacement part.
* Throttle Position Sensor (TPS): This sensor tells the computer the throttle's position. A faulty TPS can cause all sorts of idle issues, including a high idle. Cleaning the TPS is less likely to help than the IAC, but you can try it with electrical contact cleaner. Replacing the TPS is more involved and requires some electrical knowledge, as you'll need to disconnect the electrical connector. Incorrect installation can cause further problems, so a replacement should only be attempted if you're comfortable with basic automotive electrical work.
3. Things You Probably Can't Fix Yourself:
* Computer Issues (PCM/ECM): A malfunctioning engine control module (PCM) or electronic control module (ECM) can cause a persistent high idle. Diagnosing and fixing this usually requires specialized equipment and knowledge.
* Internal Engine Problems: While less likely to cause a consistently high idle without other symptoms, problems like vacuum leaks within the intake manifold or a failing valve could contribute.
Important Notes:
* Safety First: Always disconnect the negative battery terminal before working on any electrical components.
* Consult a Repair Manual: A repair manual specific to your 1993 Lincoln Town Car will provide diagrams, specifications, and detailed instructions for accessing and replacing the IAC valve and TPS. Haynes and Chilton manuals are readily available.
* Professional Help: If you're uncomfortable working on these components, or if the problem persists after trying the above steps, take your car to a qualified mechanic. Continuing to drive with a consistently high idle could damage the engine.
The IAC valve is the most likely suspect for a persistent high idle that persists after checking the obvious vacuum leaks and throttle operation. Start there, and remember to proceed carefully and consult a repair manual for guidance.
