Possible Causes and Troubleshooting Steps (Proceed with caution):
* Faulty Crankshaft Position Sensor (CKP): A malfunctioning CKP sensor can cause erratic engine behavior, including shaking and poor acceleration. A blinking check engine light without a stored code *can* happen with intermittent CKP issues. This is a relatively common culprit, but replacing it without confirming it's the problem is expensive.
* Ignition System Problems: Issues with spark plugs, wires, distributor (if applicable to your '99 Tracer), or ignition coil can cause misfires, leading to shaking and poor performance. A misfire *should* trigger a code, but again, intermittent problems might not. Inspecting these components for damage or wear is a good starting point.
* Fuel System Issues: Problems with fuel injectors, fuel pump, or fuel filter can lead to inconsistent fuel delivery. This can cause the engine to run rough and shake. While a fuel system problem often throws codes, a weak fuel pump might not always trigger one.
* OBD-II System Issues: The least likely but still possible reason is a problem with the car's OBD-II system itself. A faulty connection, a bad sensor, or even a blown fuse could prevent codes from being stored or read. Checking fuses related to the OBD-II system is a good idea.
* Transmission Problems: Although less likely with the symptoms described, transmission issues *can* cause shaking during acceleration. A slipping torque converter or other transmission problems should be considered, especially if the shaking is more pronounced at specific speeds or under load.
What You CAN Do:
1. Thoroughly check all fuses and relays related to the engine and fuel systems. A simple blown fuse can cause a wide array of problems.
2. Visually inspect the ignition system: Look for cracked or damaged spark plug wires, corrosion on the spark plugs themselves, or any obvious damage to the distributor cap (if equipped).
3. Check for vacuum leaks: A vacuum leak can disrupt the engine's air/fuel mixture, causing rough running and shaking. Inspect all vacuum hoses for cracks, damage, or loose connections.
4. Get a second opinion on the diagnostic scan: Go to a different auto parts store or a mechanic. It's possible the first scan was faulty or didn't pick up an intermittent problem. Some more advanced scanners might reveal more information.
What You SHOULD NOT Do:
* Continue driving the car extensively: Driving with a problem like this could cause further damage to your engine or transmission.
* Randomly replace parts: Throwing parts at the problem without a proper diagnosis is expensive and unlikely to solve the issue.
Recommendation: Because you are experiencing a complex issue with no stored codes, it's strongly advised to take your car to a qualified mechanic. They have the tools and experience to diagnose the problem accurately and safely. The cost of a proper diagnosis is far less than the potential cost of replacing unnecessary parts or causing further damage to your engine.
