* Transmission Problems: This is a very likely culprit. A slipping clutch (in a manual transmission), failing torque converter (in an automatic transmission), or worn-out transmission components could cause the engine to lose RPMs while the car maintains speed. You might also experience difficulty shifting gears (manual) or sluggish acceleration.
* Engine Issues: While less likely to cause a *consistent* drop at precisely 45 mph, problems like a failing ignition system, clogged fuel filter, or issues with the fuel delivery system can cause the engine to lose power, potentially manifesting as a RPM drop at a specific speed.
* Driveshaft/Axle Problems: Problems with the driveshaft or axles could cause a loss of power transfer to the wheels, leading to the engine losing RPMs. This often includes unusual noises as well.
* Differential Problems: A malfunctioning differential can also cause the engine to lose RPMs, often accompanied by strange noises or vibrations.
* Vacuum Leaks: While less common, a severe vacuum leak can affect engine performance and lead to power loss.
What you should do:
1. Don't ignore it: Continuing to drive with this problem could cause further damage.
2. Pull over safely: Find a safe location to stop driving.
3. Check your gauges: Observe your oil pressure, coolant temperature, and fuel levels. Unusual readings could point to a more serious issue.
4. Have it towed: Do not attempt to drive the car long distances with this problem. It's best to have it towed to a qualified mechanic.
5. Describe the problem accurately to the mechanic: Tell them specifically that the engine loses RPMs at 45 mph. This helps them diagnose the issue more efficiently.
The specific cause requires a proper diagnosis by a mechanic. Ignoring the problem could lead to more extensive and costly repairs down the line, or even a dangerous breakdown.
