* Throttle Position Sensor (TPS): This sensor tells the computer the position of your throttle plate. A faulty TPS can cause erratic engine behavior, including the symptoms you describe. The computer might be receiving incorrect information, leading to inconsistent fuel delivery and ignition timing.
* Mass Airflow Sensor (MAF): This sensor measures the amount of air entering the engine. A dirty or faulty MAF sensor will provide inaccurate readings to the computer, resulting in a lean or rich fuel mixture, causing power loss and rough running.
* Crankshaft Position Sensor (CKP): This sensor tells the computer the position of the crankshaft. A failing CKP can cause misfires, stalling, and erratic engine behavior, including the jumping tachometer you're experiencing.
* Ignition System Problems: Worn spark plugs, bad ignition wires, or a failing ignition coil can cause misfires, leading to power loss and rough running. The erratic tachometer could be a symptom of misfires.
* Transmission Problems: While less likely given the tachometer jumping, a problem within the transmission (particularly if it's an automatic) could contribute to a loss of power and a strange feeling in the gas pedal. However, transmission issues usually don't directly cause a jumping tachometer.
* Vacuum Leaks: Leaks in the intake manifold vacuum system can disrupt the proper air/fuel mixture, leading to poor performance.
* Fuel System Issues: A clogged fuel filter, a failing fuel pump, or low fuel pressure can restrict fuel delivery, resulting in power loss.
What to do:
1. Check Engine Light (CEL): Is the Check Engine Light on? If so, have the codes read at an auto parts store (many offer free diagnostic scans) or a mechanic. The codes will give you a much better indication of the problem.
2. Visual Inspection: Have a knowledgeable person inspect the engine bay for any obvious problems like loose vacuum hoses, damaged wiring, or anything out of place.
3. Professional Diagnosis: Given the multiple symptoms, taking your Grand Prix to a qualified mechanic is the best course of action. They have the tools and expertise to properly diagnose the issue and make the necessary repairs. Trying to fix this yourself without the proper knowledge could lead to further damage or injury.
Don't continue driving the car extensively with these symptoms. The problem could worsen, potentially causing more significant damage to your engine or transmission. Get it checked out soon.
